You want good stuff?
My personal favourite is Azumanga Daioh (hence, Azumangaman), but it has somewhat limited appeal.
You do want Fighting Spirit. That does not need to be discussed. Hopefully, you already own Fighting Spirit, but you can get all 15 DVDs at Rightstuf.com right now for cheap (although it'll cost you 100 something because, well 6.99*15...)
Boxing is quite boring to me (80% of Fighting Spirit at least) but the show is phenomenal. Its long, so it'll keep you busy for a long time. Kickass action, loveable characters, simple but unwieldingly awesome plot, you'll want it all.
You also want Haibane Renmei. HR is a really beautiful show, all 13 episodes of it. Its liscened by Geneon (RIP) so it'll be very, very difficult to get a hold of if you don't bite now. But you'll want to. Certainly not action though, more of a fantastically portrayed slice of life show.
Well, actually, BOTH shows are Geneon (Azumanga Daioh is ADV Films) so you'll need to bite on both soon!
Of course, if you have both, say so, and I'll shoot plenty more recs your way.
EDIT: And a shortlist of other series you want to buy;
Full Metal Panic? FUMOFFU- You want humour? Good luck finding something that makes you laugh this hard (maybe Haruhi)
Dai-Guard- kick-ass Mecha series thats insanely cheap and vastly underrated. Greatest OP of all time
Princess Nine- solid series about a girls baseball team. Don't be fooled by the name, its really not girly at all
Gun X Sword- stunning animation, solid plot, action and characters, with hot ladies (if thats what your after). Its a good series nobody really looks at
Kamichu- its relaxed, and a bit slow, but its a nice slice-of-life show if thats what your after. Shonen this is not.
Last Exile- I'm sure you've seen it (few haven't-or at least they've heard of it) but its good. Real good.
Genshiken- fun little show about Otaku. hardcore nerd? if so, check it out
DO NOT BUY:
Ikki Tousen
Sin: The Movie
There are PLENTY more, but I'm not in the mood to list such garbage