Get Backers, awesome stuff. And hilarious.
Peace Maker Kurogane, pretty cool, and funny at times.
Trigun, one of my personal favorites. Great action, hilarious comedy, and great storyline.
Hellsing, also at the top of my list, it's just awesome in all aspects. Vampires and such.
Evangelion, very thought provoking, good action, but not for the weak minded, it is EXTREMELY intense, especially near the last few episodes. Trust me, it's good, but only if you can handle it.
Zoids, another of my favorites, it's hilarious, giant fighting animal robots, tournaments, wars, great storyline and characters.
I've seen a few in my time.