The offical site by the staff at Mirage. Full of information about the comics, cartoon, and more. You can ever buy some back issues. A great site to start with.
Not an actual Turtle site, but probably the best way I've found to find figures. And a search of the auctions will give you a better idea of the going price for figures than any price guide I've seen.
If there is another site you'd like me to add, let me know.
tmntman@tds.net