There's Shas'O'Cam's http://s10.invisionfree.com/gravtankonline for 40k in general, however it focuses on Eldar, Dark Eldar and Tau- the grav tank users. Sorry for posting this shas'o'cam, just had to tell everyone- it's quite a good site. Has anyone got a good Chaos one?
Here are a couple more from the guy that started everyones favorite E-zine, Firebase. I would deffinately suggest putting these in a sticky. The Bell is updated daily while the Tau and Wolves are updated fairly regularly.