Adventurers! lampshaded this (along with a similar trope) once or twice. The above quote was given after one of Eternion's lackeys pulled a sword from behind his back that his taller then him.
Eternion: This planet makes storage a snap.
The Adventures of Dr. McNinja: Doctor McNinja makes frequent use of a large grappling hook, but it is never seen on his person except when he throws it. The same applies for Sean when a grappling hook pops out of his hand (in the crapsack future, where he's become a "technomage" with a power glove).
And subverted here, where young superhero Summer explains that girls with super-strength aren't allowed to use hammers, since they might cause actual damage instead of comic damage. Instead, she has an alternate weapon: a flyswatter, which she uses to swat the offending young man on his fly.
In Flying Man and Friends, Mr. Stinky is able to produce (among other things) a gun out of nowhere, despite not wearing clothes or having a place to store anything.
Often used in Girly where Winter pulls out giant dildos and bazookas out of nothing, while Otra pulls out spaceships and her own armor with accommodating sword just like that. And one of their adversaries use the hammerspaceagainst them while referencing to this very trope. While using a hammer.
Let us not forget that Susan has ability to turn realspace into her own personal Hammerspace thanks to magic powers.
Later on when Susan finds she can't summon the hammer, they find that the immortal who created the relic that allows girls to summon the hammer is about to reincarnate himself, undoing the magic.
In a couple more recent pages of Grim Tales from Down Below, Hammerspace has played a major role in the appearance of objects such as: An iron engraved with "STFU" on the side, a kettle with the word "FAG" on it in a similar vein, a ball gag, a cherry, a knife, a spontaneously changing outfit, and a paintball gun. It's not as kinky as it sounds.
Also, Dave's cigarettes come from hammerspace. At one point before Dave didn't start smoking, Helen realized she was turning into Dave when a cigarette popped.
Half the equipment owned by The Order of the Stick (especially V's familiar) just appears out of nowhere. In the case of the familiar, this was to represent the way actual DnD players tend to forget their familiars even exist; on the other hand, Elan producing the Girdle of Femininity/Masculinity leaves far more questions.
Lampshaded when Haley and Roy switch weapons, and he fires a single arrow (which was already nocked when he got it) from her bow - then realizes that he has no idea where she keeps the rest of her ammunition (she is never seen wearing a quiver).
In Ozy and Millie, Ozy goes out in a cold snap before his winter coat comes in—the result is that it comes in all at once, leaving him extremely fluffy. Millie takes advantage of this to hide things in him, up to and including a piano.
A Pinkish Blue: In this Comic you expected the boy to draw out a proposal ring, which would at least kinda make sense, but then he draws out a present bigger then his head...
Justified in Power Of Ether as the main characters all have portable pouches that can, quote, hold about 1 cubic meter's worth of stuff inside. However, they apparently damage organic material severely. (Note, this quote is from the semi-retconned first chapter, but it still applies)
Dax:Your hands will be okay for a few minutes, but put your head in and you'll quickly go blind.
In Roses and Thorns, scientist Joseph Umbra renamed hammerspace as "Umbral Science", after gaining a monopoly on the technology used to access it.
In Sluggy Freelance, despite wearing no clothes whatsoever, Bun-bun is always able to produce his switchblade at a moment's notice.
Gwynn likes to keep a baseball bat in impossibly small places like a cookie jar or her purse in case she needs to beat up Torg or Riff for being stupid.
Also Bun-bun's gun. Lampshaded when he was talking to Oasis (the gymnastic assassin).
Bun-bun: You know what, toots? You keep throwing your knives and stars at me, and I just gotta ask. (Pulls a gun out of nowhere.)Where do you keep all your weapons hidden?
Used frequently and by name by the weapon-happy Petra of Okashina Okashi (Strange Candy). She allows the other characters to store things there, mostly clothes, but she seems to be the only one of them who can access it.
In Yokoka's Quest, Misha has access to a "storage dimension", and is shown keeping a bag and a small parcel there (the bag itself is presumably a normal bag and not a Bag of Holding. Suggested to be a common ability, by Misha stating that familiars are expected to do use this to carry their master's belongings, and her presumption that Yfa can also do this (he can't). Clothing seems to also go into hammerspace during most shapeshifting.