I've gotten all my skins and wraps from
The Lucky Labs. Really great quality and excellent customer service, and their prices are very reasonable. They have a discount code --
newipad35 -- good for 35% off your purchase, expires on March 24th.
As for cases that will work, most if not all bumpers should be fine since they don't affect the back of the phone. But since the skin will make the phone thicker, most full-body cases will probably be too tight. Some snap-on cases will fit, some won't; for instance, the Agent18 SlimShield works fine for me with a skin on, but the Incase Snap doesn't.