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 paint ball gun. It's not as kinky as it sounds.
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.
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.
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.
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.
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).
ThisDaisy Owl comic lampshades it. "I am kind of alarmed at how quickly you just produced that pie."
In Brat-Halla, Sif produces a war god's giant club from her purse when she thinks another woman is flirting with her unrequited crush.
Eddie from Emergency Exit makes good use of hammerspace on a regular basis.
Lampshaded with hilarity in this strip of DM of the Rings. "You don't have a backpack. What you have there is an invisible leather TARDIS."
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.
The Mansion of E features the Hammerspace Company who deals in extra-dimensional storage.
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.)