There are tons of anime to watch, provided you have time to read/watch.

These are some of the anime's that I have watched and enjoyed. I would keep updating,

Super Natural, Adventure

One Piece
Naruto
Hunter X Hunter
Bleach
Fairy Tail
D-Grayman
Claymore
Dragon Ball Z

Sci-Fi

Steins;Gate

Action, Mafia

Noir - Awesome background score
Gun Grave - Friendship
Gangsta - Mature
Black Lagoon - Mature
Baccano! - Mature
Darker than Black - Clueless

Space Adventure

Cowboy Bebop - Cult
Trigun - Selfless
Planetes - Unique
Sidonia no Kishi (Knights of Sidonia)
Eureka 7

Mecha

Full metal Panic !
Mobile Suit Guntam

Psychological Thrillers

Death Note
Psycho-Pass
Code Geass
Monster

Detective

Detective Conan - (Case Closed)
Tantei Gakuen Q (Detective Academy Q)

see now:

Racing

Capeta - Realistic
Initial D - Kamikaze level racing

Samurai

Rurouni Kenshin (Samurai X) -
Samurai Champloo - Slapstick
Afro Samurai - Mature
Basilisk - Mature

Virtual Reality

Sword Art Online - You will love it
Btoom! - Virtual game turned real life
Overlord

Sports

Eyeshield 21 - American Football
Haikyū!! - Volleyball
Cross Game - Baseball
Baby Steps - Tennis
Hajime no Ippo - Boxing
Kuroko no Basuke - Basketball
Slam dunk - Basketball
One Outs - Baseball
Major - Baseball
Ookikku furikabutte (Big Windup !) - Baseball
Ace of Diamond - Baseball
Hungry Heart Wild Striker - Football
Knight in the Area - Football

Real life

Gin no Saji (Silver Spoon)
Honey and Clover

See now: Animebis

Martial Arts

History's Strongest Disciple

High School Life

Great teacher Onizuka (GTO)
Hyouka
Another
Clannad
Haruhi Suzumiya's melancholy