Hm...
In addition to Tezuka manga,
I also enjoy Kindaichi Shounen no Jikembo, AKA Kindaichi Case Files.
It's a wonderful mystery manga. The characters are memorable, the mysteries are tough, and there's a fair amount of humor mixed in.
Yu-Gi-Oh! is another one of my favorites, but pretty much everyone knows about that... ^^;
In the way of american comics, Jhonen Vasquez's comics are some of the best that I've seen. ^^