I have all of the Ultimate Marvel stuff in some form except for the most recent stuff that I don't have but will be getting in trades/hardcovers. Right now I'm getting Ultimate Spidey, New Ultimates, Avengers 3, and X in individual issues. I'll be getting the Enemy series collected.
I have all of the major Image/Devil's Due GI Joe books in singles except for the Data Desk Handbook #2 N-Z. I don't have the trades that sometimes had a few extra pages here and there.
I have all of the new IDW GI Joe books in singles. I'm also getting the main Marvel series reprints. I haven't gotten the Special Missions reprint books because they didn't confirm that they were actually going to be releasing them all. I also haven't gotten the "best of" books because they're pointless.
I have a sizable chunk of the 80s/90s GI Joe Marvel books. I've got all of the major (and many less major) side story books including the complete Special Missions. I've got a good chunk of #1-155, but I recently stopped actively pursuing them because it appears IDW is going to complete their reprint series. I have Marvel's incomplete reprints from 2002, too. Yeah, I have duplicate books in that I have IDW's versions, but I decided to vote with my dollar early on to get IDW to complete the reprints this time. In addition, I have the cheaper and nicer reprint Tales of GI Joe version of #1, so I have the Hot Potato story that for some reason hasn't been reprinted since that very book in the 80s.
I'm not a big DC fan, but I have a handful of books here and there. My favorite is Red Son. I've also been getting the newer Sgt. Rock miniserieses from the past decade or so.
I had a big manga boom about 5 years ago, but now I only really read Tsubasa, xxxHolic, and Suzuka. Tsubasa's coming to an end soon, too. It already ended in Japan. I got a lot of CLAMP manga.
I like picking up the odd single volume trade or hardcover, too. Scud, V For Vendetta, Bone, The Originals, etc.
EDIT: I should add that I don't collect for the sake of collecting. I read everything I buy. If I won't read it, I won't buy it.