Everything I like (the one anime and the two manga... Plus the 8,000 video games...) are things no one's heard about or paid very much attention to, it seems. 8D;;; Uhh, well. Rozen Maiden is my favorite anime/manga, and Et Cetera is a close second for manga. I guess you could add Karin/Chibi Vampire in there if you want, but it's really cheesy. My favorite game is Tales of Legendia...
As for things you could probably sell fairly well? Um... Everyove LOEV Twilight, so you could make, like, bookmarks of those characters or something. Then for a joke you could do some Mudkips stuff. Anyone who gets the joke will laugh or buy something, and then the Pokemon fans who don't get the joke will be like, "Omg! I luv Mudkips!!!!" as other people have mentioned, Haruhi Suzumiya and Death Note should sell pretty well. Oh! Phoenix Wright things should actually sell okay too, and I might be included in buyers. 8D; If you draw and HAWT SEXAY PIN-UPS I'm sure you'll get a few buyers for generic things like that, too...
I'm sorry I don't contribute much... 8D;;;; I hope this helped a little bit, though. But I will add that if you do anything Death Note the fans will be all over you like fruit flies. If you were like, a moldy peach or something. Yeah...