Kodomo no Jikan. >;D
Ok, but seriously, right now I think the one topping the list is a close call between Gurren Lagann and CLANNAD[footnote]mostly because I haven't finished After Story yet, when I do It'll probably be on top.[/footnote]. But honorable mentions go to Soul Eater, Azumanga Daioh, FLCL, Rozen Maiden, K-ON!, To Aru Majutsu No Index and a few more I can't think of right now.