i'd probably say anything that has to do with naruto..personally i don't like the show or anything, but the merchandise seems to go fast because i see so many people with headbands/etc...get a second opinion, though, i'm not infallible!
i enjoy buying whole enitre series in box sets or just as many episodes as you can fit into one box set i just dont like having tons of dvds of the same show
The box sets are the way to go right now. Viz media figured that out with naruto and I've got every box set out so far. Some of my suggestions for what people should get are the death note dvd's and the melancholy of haruhi suzumiya dvd's because they got some nice extras even though they don't come in box sets yet. Oh yeah, Bleach is going to get a box set with the first 20 episodes (which I think came out yesterday) which is a must-get for bleach fans.
I say like xixspazxix say's, naruto anime collectables sell fast these days. I also don't really watch the show even if i just buyed a naruto headband, which is for my sister. I also say that the melancholy of haruhi suzumiya collectables sell alot too. Figurines are an example, i own three figurines from the show.