The correct answer is, of course, Azumanga Daioh. Funniest show I've ever seen. Kareshi Kanojou no Jijou (usually translated into English as His and Her Circumstances) is also pretty good at first, although it goes downhill after about episode 13.
Edit: I should add, though, that the humor in the above two shows is somewhat different than that of Excel Saga, so it may or may not be your cup of tea. You should give the above two shows at least a couple episodes, though (if I recall correctly, the first episode of both is a little bit weaker than the following episodes).
Edit: I should add, though, that the humor in the above two shows is somewhat different than that of Excel Saga, so it may or may not be your cup of tea. You should give the above two shows at least a couple episodes, though (if I recall correctly, the first episode of both is a little bit weaker than the following episodes).