Manga University

If you like manga you surely now Manga Univerity.

There's also a pretty good website, that I'm not sure if has been created by Manga Univerity (correct me if it's not), called OMU ( Online Manga University) which was created in August of 2000.

These two websites have tutorials on how to draw manga, online stores and many more cool and useful things.

Both sites are free to use.