Konata Izumi from Lucky Star. ^^ She's my avatar, so naturally I like her.
Haruhi Suzumiya from... well Haruhi Suzumiya. Moody, cheerful, abusive and hyper, what's not to like?
And finally, Lina Inverse from Slayers. The sorceress swordsman, enemy to all that live and the dragon spooker... she...