I don't watch anime. They suck. I read manga. (Only anime that is better than the manga IMO is Gintama.)
So READ
Monster (fantastic, amazing, godly, sextastic series)
Fist of the North Star (guaranteed to make your balls grow bigger, due to massive amounts of manliness.)
Vagabond (samurai series, really cool.)
Adventure Boys (Slice of life series, mangaka is looking back at his youth.)
Trigun (no shit sherlock)
Love Hina (guess why?)
20th/21st Century Boys (Dunno how to describe them that well... just plain cool series)
Biomeat Nectar (awesome horror series)
Blue Heaven
Alive
(these 2 are trippy psychological - horror thrillers)
Bokurano (THE BEST GIANT MECH SERIES EVER) The catch is that its 15 kids that control it thru 15 battles, and it takes the controllers life at every battle.
Yankee-Kun to Megane-Chan (Hilarious comedy series)
Hellsing (trigun with vampires)
I like Zatchbell, but Im weird like that.
Change 123 is a more action oriented love hina basically.
Chrono Crusade is a more shonen trigun (the ending made me cry.)
Majin Tantei Nougami Neuro is a comedy action mystery series that rocks.
Hajime No Ippo is the most badass thing ever. Its a boxing manga. Thats badass.
Skyhigh: People die, and have 3 choices, kill someone and go to hell, go to heaven, or be a ghost. What do they choose? Its an amazing series.
The World is Mine: Fucking trippy story of 2 serial killers and a HUGE (Godzilla sized) bear that wreak havoc across Japan. This series is amazing to say the least.)
And those are my favorites
My 2nd tier ones... nother story for another day. I read through like 1 complete manga series a night lol, I am so addicted.
And all but Trigun and Hellsing can be read at onemanga.com
So go get reading!!