Stegosaurs have always been one of the dinosaur groups with only a little number of species described (this cannot be told about their relatives the Ankylosaurs). This explains the shortness of this dino-page despite the notable fame of this dino-group. Also note that all the examples below are outside North America; indeed, only one kind of stegosaur is known from this landmass with sureness, the everly-popular Stegosaurus. Another North American genus was described in the 2000s, Hesperosaurus, but it could be another Stegosaurus species. A third genus, "Diracodon", was named during the Bone Wars, but now is regarded as an invalid synonym of "Stegosaurus". Among non-stock stegosaurs you've better chances to see Tuojiangosaurus and Kentrosaurus, but could also meet Dacentrurus, Huayangosaurus, Wuerhosaurus, Lexovisaurus, and other relatives, as well as getting the "Dravidosaurus" mentioned. All this, at least, in dino-books and paleo-art...
...Indeed, if you're watching a film or even a TV documentary, good luck if you’ll ever find a stegosaurian which is not Stegosaurus. However, if you do, it would probably be Kentrosaurus.
Only half the length of Stegosaurus, its overall body-shape was almost identical to the latter… except for the armor. The usual plates on the neck and back were much smaller and paired (not zigzaging), became gradually spikes on the hip and lasted with at least five pairs of true spikes on the tail. But this is not all, Kentrosaurus had also a pair of isolated spikes arising from its shoulders. A Late Jurassic animal like Stegosaurus, Kentrosaurus was discovered in the 1910s in the same Eastern-African site along with with much bigger dinosaurs like Giraffatitan. Dozens of Kentrosaurus skeletons have been discovered, but with plates/spikes scattered away (as usual among stegosaurs): thus, scientists once thought Kentrosaurus side-spikes were on its hips instead of its shoulders. That's why classic dino-portrayals show it with spikes protruding from the pelvis instead of from its forequarters.
One mention about [mis-]spelling: Kentrosaurus should never be confused with Centrosaurus . Both names mean “pointed lizard”, but the “points” of Centrosaurus were on its head: it was a ceratopsian. In some old sources Kentrosaurus is known as "Kentrurosaurus" ("pointed-tailed lizard"), but this name is now invalid.
I've some cousins in Europe: Dacentrurus & Lexovisaurus
Other two similar-looking but larger porcupinosaurs are known from Middle Jurassic Europe: Dacentrurus and Lexovisaurus, both found in several european countries (England, France, Portugal) Dacentrurus has the distinction to have been described before Stegosaurus itself (in the middle of the 1800s), while Lexovisaurus was named in full XX century. Unfortunately, both are known from incomplete remains, and we are not sure about their precise look or even their size. Some suspect Dacentrurus was a very large animal, maybe even bigger than Stegosaurus itself (which wouldn't be the largest stegosaurian as traditionally said). While Dacentrurus is surely similar to Kentrosaurus, Lexovisaurus is in some portrayals shown more similar to the Chinese Tuojiangosaurus (see below).
Recently, many alleged "Lexovisaurus" remains have been reclassified in another genus, Loricatosaurus. In 2009, a brand new stegosaur was excavated in Portugal: Miragaia. With its small but abundant plates and unusually long neck, it incidentally resembles the "Dinny" character of the comics Alley Oop.
The unpronounceable: Tuojiangosaurus
Together with Kentrosaurus, the most portrayed non-stock stegosaur in popular dino-books has been Tuojiangosaurus — don't worry if you cannot pronounce that "jiang" correctly, unless you are Chinese or Chinese-speaking of course.
Discovered in the 1970s, Tuojiangosaurus was basically an Asian variant of Stegosaurus, a bit smaller and with a rather intermediate armor between Kentrosaurus and Stegosaurus: narrow, paired plates like the former, but the usual four tail-spikes (thagomizer) like the latter. With such small plates, it’s hard that Tuojiangosaurus and Kentrosaurus would have used them as solar panels or radiator, unlike what was possible for Stegosaurus. Some portraits show the tuojiangosaur with shoulder-spikes like those of Kentrosaurus, but we are not sure it had them.
Together with the carnivorous Yangchuanosaurus and the sauropod Mamenchisaurus, Tuojiangosaurus is one of the three classic dinosaurs from Late Jurassic Asia; however, this "Chinese Trio" has yet to appear in recent CGI documentaries. On the other hand, the tuojiango seems expecially common in english popular dino-books, as one beautiful skeleton of it has been built in the Natural History Museum of London since the 1980s; this mount is often shown in illustrations - even though it appears quite incorrect to us, with its splayed limbs and low-slung neck and tail.
I've still other cousins in China: Huayangosaurus & Wuerhosaurus
China has gifted to us about half the steggies around the world. Other than Tuojiangosaurus, there are: Chialingosaurus, the first discovered (years 1940s), similar to Kentrosaurus but more slender than other Stegosaurs; Chungkingosaurus, one of the smallest known stegosaurians (3-4 m long); the big-headed, long-limbed Huayangosaurus (see below); , and the large Wuerhosaurus, similar to a short-plated Stegosaurus. A recent find has been called Gigantspinosaurus, due to its gigant[ic] spines on its shoulders (of course, it's not a cross between a giganotosaur and a spinosaur!).
Huayangosaurus is worthy of note because is the most primitive stegosaur known from good fossil material. Only 4 m long, it still preserved several ancestral traits in its skeleton, such as small frontal teeth on its upper jaw (a typical primitive trait among ornithischians) which were lost in more evolved stegosaurs. Its armor, however, was already fully-stegosaurian, similar to Tuojiangosaurus but also with shoulder-spikes like Kentrosaurus.
Robinson Crusoe dived into the sea: Dravidosaurus
Definite stegosaurs appeared in the Middle Jurassic with kinds such as Huayangosaurus. Reached their highlights in the Late Jurassic with Stegosauruses Tuojiangosauruses Kentrosauruses and whatnot. But they began their decline in Early Cretaceous, maybe because of competition from the more armored Ankylosaurs; Wuerhosaurus is the most well-known among these Cretaceous kinds.
However, there was a stegosaur which, uniquely, reached the goal to been hit by the comet: Dravidosaurus. One of the few dinosaurs discovered in India (which was a huge island in Late Mesozoic), the dravidosaur somehow managed to land on it, and flourished there thanks to absence of competiton which other relatives faced in the mainlands. Its status as “The last Stegosaur” gave it several mentions in old books and also some documentaries. Well, all this has collapsed in the worst way possible. In 1996, a re-examination of its extremely fragmentary remains has revealed our Robinson Crusoe-saurus to be 1) not a stegosaur, 2) not a dinosaur, 3) and not even land-living. It was a MARINE REPTILE, more precisely a PLESIOSAUR.