There are innumerable brands of hot sauce out there with names like Torch, Hell's Breath, and the like. Most are the same sauce - as in made at the same time using the same recipe and by the same manufacturer. This naturally hasn't stopped hot sauce aficionados from getting into huge fights over which is the best.
There are several real-life hot "sauces" that aren't actually sauces at all. Many manufacturers whose hot "sauces" skirt the upper limits of the Scoville scale advertise special "pure capsaicin hot sauces" that are actually made of pure capsaicin that has been diluted with water or vegetable oil. However, such "sauces" are lethally toxic and thus are not intended for actual human consumption. They are novelty collector's items, not actual condiments, and thus only technically qualify as examples of this trope.
A restaurant in Tallahassee, Florida, was once shut down by the Leon County Health Department on charges of toxic chemical contamination (and the owner cited for Reckless Endangerment) after they began featuring food that had been "spiced up" with one of these additives. These things will kill you if you ingest too much of them.
"Pure cap" can be legally sold as a food additive. That is, you're supposed to add it to things in quantities like "a teaspoon per gallon". You are NOT supposed to actually use it as a condiment, or leave it sitting around where some idiot could do so.
A good rule of thumb about pure cap and additives of that scale is that unless you're dealing with large quantities of food, use the smallest dosage possible, say one crystal (such as the type that capsaicin forms when pure)
Consider the Naga/Bhut Jolokia pepper (AKA the "Ghost Chili"), the hottest pepper in the world. It has a Scoville Scale rating of 850,000 to 1,500,000 (compare that to a Jalapeño, which has a Scoville rating between 2500 and 8000, or even the Habanero pepper, which tops out at 350,000). You have to use protective gear to cook with this thing, and that's not a joke: they're literally hot enough to irritate skin. Cooking with them in the traditional sense is impossible. Most people in Bangladesh, from where the breed originates, only dip it into the cooking pot for a few seconds, while smearing the rest of the pepper on their fence as an elephant deterrent.
It has been upped in March 2011 by Trinidad Scorpion "Butch T", Guinness World Records attest. And this is already pushing it toward genetic engineering (i.e. not something that grow naturally in some place).
Do note that these are not technically the hottest substance found in nature; some plants have extremely pungent substance called Resiniferatoxin that ranks at 16 billion Scoville. Such substances aren't capsaicin and probably should not be used as condiment.
In Minneapolis, there's a place called Marla's Caribbean. It serves Ghost Pepper Wings - buffalo wings made with ghost pepper sauce. Bear in mind, ghost pepper is usually applied with an eyedropper.
The "-toxin" ending is a big clue here. It turns out the substance can literally kill the nerve cells responsible for the sensation of pain, so it's being looked into as a potential treatment for sufferers of chronic pain.
The phaal is a British speciality whose selling point is that it's basically chicken in Blazing Inferno Hellfire Sauce. Most curry houses don't actually list it on the menu but will serve it if you specifically ask for it; the staff will look on warily as you eat. If it's anything to go by, it's hotter than the vindaloo, and even that's overpowered to the tongues of many.
According to Jasper Carrott, the phaal is so called because the usual response after eating it is "FFFFFFFFFFFFFF... I'll be all right...". The Geordies attempted to one-up it with the even hotter 'magmaloo', which according to Carrott comes in a bowl made of Space Shuttle re-entry tiles, comes with a side order of Savlon, and has a tendency to melt spoons. And fillings.
Another legend is that "phaal" is a Bengali word meaning "stupid drunk white man".
Burns victims often say that when they are actually on fire, there is no pain. It has something to do with the body pumping out adrenaline in such vast quantities that the nerve endings stop working. Well, it wasn’t like that for me. The pain started out mildly, but I knew from past experience that this would build to a delightful fiery sensation. I was even looking forward to it. But the moment soon passed. In a matter of seconds I was in agony. After maybe a minute I was frightened that I might die. After five I was frightened that I might not.
Even Tabasco sauce (comparatively mild to most everything else on this list) has some rather impressive corrosive properties. It is said that the forklifts used to transport the oak barrels in which the stuff is aged have to be replaced every two years, because the Tabasco mash eats through the forklift blades.
An episode of Mythbusters featured Adam and Jamie testing whether hot sauce (like common salsa) could be used to break out of prison by corroding the iron bars. The result was that with enough time (which is a lot if you are in prison) it is possible to break the bars with salsa. Jamie also showed that with a little DC current from a radio (like if the inmate smuggled one in) you could potentially speed up this process since the salsa was a good conductor.
It is important to point out that hot sauce also contains citric acid and, often, vinegar. Many forms of salsa also contain a good deal of salt, which has corrosive properties in the right circumstances.
Any metal corrosion caused by Tabasco is due primarily to the vinegar. Capsaicin has no effect whatsoever on metal. Or birds, which lack the sensory receptors for it and will happily eat peppers that mammals (which do have the receptors for it) avoid as if they were on fire. Which is probably the reason why hot peppers evolved like that in the first place; birds will spread the seeds over a much wider area than mammals do.
Wasabi sauce is another notable variant. A Japanese team won the 2011 Ig Nobel prize for chemistry for patenting a fire alarm for the deaf that sprays out aerosolized wasabi. The smell of wasabi can wake up sleepers in under 10 seconds.
While clever, such an invention is sadly kneecapped by wasabi's notoriously short shelf-life.
And horseradish, western cousin of wasabi. Especially one sauce used in Ukraine - it is mixed with Russian Mustard, which is damn hot already and an extra helping of salt. It does taste good with borscht, if you apply it in a fin layer on bread.
If anyone is curious, the compound responsible for the hotness of mustard, horseradish, and wasabi is allyl isothiocyanate.
Certain parts of Africa cover up the low quality of their beef by cooking it in a concoction known as "pepper soup" using small wild peppers which seem to only be used for that purpose. It is successful in covering the taste of the beef, as well as everything else for the next week.
There's also been some research indicating those hot peppers can stave off food poisoning, which may explain their popularity in places where the heat makes food and water a bit suspect.
And planting chilies around the edges of your fields is a great way to keep elephants off your crops, precisely for this reason.
Korean kimchi. Several varieties are just painful to even smell, let alone eat. South Korea has very low rates of intestinal parasite infection and tooth decay, but also high rates of stomach cancer.
Several regions in China are known for having extremely spicy cooking due to a combination of weather conditions, availability of spices, attuned palates and the occasional need to mask less than optimal ingredients. Sichuan cuisine in particular is infamous and a local joke says the people there essentially worry that a dish isn't spicy enough, though the peppers responsible for the heat (and the blood red color of dishes that use lots of it) also have a numbing effect.
Hunan cuisine is related, if differing slightly in the fine details; Sichuan's numbing heat involves the use of peppercorns, whereas Hunan cuisine has no compunctions about constantly reminding its consumers of its spiciness by virtue of pure chili volume.
Some... people... believe that hot spices can cure or worsen cancers.
Blair's, who created the one that illustrates the main page. Best part? It's not even their strongest. (they even made a limited edition product with pure capsaicin, reaching 16 million Scoville units - something comparable to pepper spray)
Maitland, Florida restaurant Tijuana Flats, whose hottest sauce (Smack My Ass and Call Me Sally - Chet's Gone Mad) is about 1.5 million Scoville units, more than enough to actually feel burning on your skin if you placed some on there.
Nicko McBrain's restaurant Rock N' Roll Ribs (also in Florida, Coral Springs). The escalation even uses songs from Nicko's band to lampshade: it started with Mild, Medium, Hot, Run to the Hills. Then it became Mild, Medium, Hot, Die with your Boots On (which replaced RTTH after one complained it wasn't hot enough), and Heaven Can't Wait.
Mustards usually don't go as hot as pepper-based sauces, but Russian mustard takes the cake. Even in small quantities it's a fine (but not nice) cure for snuffle.
Many restaurants specializing in hot wings will offer some sort of challenge to anyone who can eat a certain number of their hottest wings in a fixed amount of time. Some up the ante by saying that the customer is not allowed to consume anything else within five minutes that would counter the burn.
To unsuspecting continentals, especially Germans and Frenchmen, English mustard can do this. Americans raised on that bright yellow concoction hot dogs are slathered in are also susceptible. Those that aren't warned off by the vivid yellow color tend to sorely regret applying the same quantities of English mustard as they would of their native blends.
Please note: if it comes out of a jar, it's adulterated with stuff to make it shelf-stable and spread better. 'Real' Colman's mustard is a yellow powder - of pure powdered mustard seed. Made into a thin paste with water per directions, two teaspoons is enough to make a plate of mashed potatoes into yellow mouth-napalm.