Definately worth your time (if you're into the action/comedy genre):
One Piece - Always and forever my #1 favorite. Pirates, slapstick, adventure and drama that has brought most of my guy friends to tears. XD
Grenadier - New! But it does feature a girl kicking more a** than the male lead character.
FullMetal Alchemist - Funny, smart, and great animation. What more do you need?
Samurai Champloo - Nicely animated with a touch of humor. Plus you get Samurai action? What else do you need? Plus Kazuya-sama does some voice-acting in it. XD
Nice (if you're into serious action):
Berserk - If you haven't seen this, you're missing an epic. The manga is WAY better than the series, plus there's a beautious game coming to PS2.
Pretty good (if you just like blood and shameless nudity):
Elfen Lied - A short but sweet series in the horror genre. I didn't find it very scary, but cute girls ripping men (and women) limb from limb is pretty entertaining. Plus the first episode is like %90 nude women. Come on guys, you know you wanna watch it.
Tenjou Tenge - The manga is borderline hentai, but I love it. Chicks (like me) enjoy the action, guys like the shameless shower scenes. XD The anime was pretty good, 24 episodes, but they better continue the series eventually. o.o;
Tsukiyomi - Moon Phase - I'm starting to like the series, the cute girl as the vampire and the guy as the damsel in distress is a pretty neat twist.
Everything else (that I enjoy):
Great Teacher Onizuka (GTO) - I like this series alot, but some say it's an aquired taste. It's education like you've never seen it before! XD Plus there's some great scenes in the anime. The manga differs ever so slightly.
Tactics - It reminds me of Yami no Matsui, and I enjoy my (kinda) Shonen-ai series. It's got great animation and many bishies. Plus it's cute and funny.
It's a buddist-themed demon-beat-'em-up with what seems to be a deep plot.
Kyou Kara Maou! - I eagerly await each episode of this hilarious Shonen-ai show. Guys should check this out as well, it's just so...wrong! I love it, and I get alot of laughs out of it, plus the story seems to be pretty deep (I hope), and I wish it'll keep going after 26 episodes (currently 23 available, thanks AonE).
That's it for now. XD Just some of my personal faves, plus there are the obvious popular series like Naruto. And others that are good, but I didn't go into detail, like Sunabouzo. Anyways, there's alot out there, you've just gotta try 'em out.
I'll stop rambling now, it's my habit to post short essays rather than small messages. XD You should see me in a chat room.