My favorite is, by far, One piece. I like Kenshin (the Shishio chapter) and Saint Seiya (not the new series). As a big fan of Transformers, I love Superlink and Galaxy Force.

I've always have a great interest in Studio Ghibli productions, and mostly in Hayao Miyazaki (My Neighbour Totoro, Porco Rosso, Mononoké, Nausicaa, Chihiro...).
As for anime series, I really enjoy the fact to watch them for free. Most of these animes are not available in french, so fan translating teams do a wonderful job on it. And the series can be online and downloaded without any legal issue, until one of the series is licenced in France of course.
Recent animes I've watched those years: GTO, Blood+, Death Note, Welcome to the NHK! (great great anime, I strongly recommend it), GUNxSWORD, Baccano, and I surely forget some.

+1 to fellow OP fan :)
A friend of mine is a huge fan of Hikaru no Go. He says i must check it out. anyone seen it?

I'm a fan of anime. Can't stand most of it today though because it seems... devoid compared to the older stuff.
Favorites are:
Gungrave
Blue Gender
Escaflowne
Evangelion
Trigun
Outlaw Star
Cowboy Bebop
Gunslingr Girl
Kenshin
Elfen Lied

Anything from Satoshi Kon hits me like a 2*4 to back of the head. And after them I feel like having been hit by one minus the pain. Good stuff
Also Haibane Renmei is alltime favorite.

Don't really watch Anime these days but those I enjoyed are:
1) Gungrave
2) Monster
3) Full Metal alchmist
4) Mobile Suit Gundam (yes, the first in the series)
5) FLCL
For Manga:
Vinland Saga
Team Medical Dragon
Death Note
Historie
One Piece
Eyeshield 21
Mushishi
Pluto

Tengen Toppa Gurren Lagan is the most epic and awesome series ever. The music, the characters, the complete over-the-top-ness. It's madness =D
Glad it got mentioned already.
Another high quality production is Eureka 7. High production values, very convincing characters, no black and white morality and.. Robots. Surfing. In the air. Give the first few episodes a chance though. Somewhere along you'll realize you're watching one of the best anime ever.
Soul eater is a recent show which is a lot of fun. Every episode is fun *and* relevant, the characters are varied and the art is stylish.
Deathnote is very good if you just stop watching after episode 25.
Other great series *really* worth checking out:
Real Drive (very sweet, pretty visual style (girls with realistic proportions!))
Tetsuan Birdy Decode (A two-minds-in-one-body series which manages to NOT fall for all the cheap gags, in the second series the action scenes are reminiscend of those in Noein (spoiler, I suppose))
Baccano! (just watch the intro and you're sold)
Ouran Host Club (a parody of the "1 girl, lots of 'sexy' anime boyz"-genre which actually also manages to tell a story in the end. This one just made me laugh a lot =D )
And of course more classical examples like cowboy bebop, trigun, FLCL, most of Studio Gibli's work.
EDIT: removed the link to the Baccano intro, since it wasn't the actual intro. Seems impossible to find 0_o

I recommend watching Dragon Ball Kai.
It is remastered version of DBZ. They removed all of the filler crap :) it is pure animated manga.
so no more powering up for 2 episodes, starring at each other for five minutes, pointless chatter, filler scenes
Currently it is on episode 17 and they are already leaving for namek. the whole series should be finished under 100 ep.

Take the good parts of Harry Potter, the good parts of Dragon Ball and a healthy does of fanservice and you'll get Mahou Sensei Negima. A 10 year old boy (who happens to be a mage from Wales) gets assigned to a japanese all-girls school as a teacher. While the first 15ish chapters are slow and could be confused with your average harem manga, it quickly turns into a fairly high octane shonen series.
Additionally I'm currently reading One Piece (the manga, not anime) and reading/watching Naruto. I try to catch up on Hellsing Ultimate whenever there's new stuff. Have watched and enjoyed Akira, GitS (the movie), TTGL, Gunbuster, Bubblegum Crisis, GaoGaiGar and Samurai Pizza Cats.
Samurai Pizza Cats (US version of Kyattō Ninden Teyandee) should be required for anyone who whines about dubs and altering the story for US/Western audiences.

Here it is.
Great opening for a great anime.

Thanks for mentioning that. I've wanted to rewatch it for old times sake, but I really was put of by the ridiculous number of episodes. It's a nice show, despite it's age and obvious flaws. Plus I hardly watch any of the pure shounen shows anymore, so this will be a nice change.
Ah. Nice job. Now everyone, go watch!
EDIT: also, Tokyo Magnitude 8.0 is indeed very nice.

http://thechive.com/2009/09/japanese-teen-bedrooms-are-perfectly-normal-not-weird-20-photos/

dont watch gantz the ending sucks

oh lol
i think he is already done with gantz

Haha, yeah I finished Gantz before school ended last year. At first I didn't really like it, but then the more I think about it the more I like it. The same thing happened when I watched Witch Hunter Robin.
Now I am probably going to watch Gankutsuou which I have heard great things about.