I prefer the more natural looking ones from Petco, like so:
I have the XL one of this actually
Then, if you're going for the minimalist approach, Reptile Basics has some nice ones:
boring haha
This is something I recently found and love the idea of:
cool
And if you're a complete cheapskate (jk :P), you can cut a hole in an overturned terra cotta pot or tupperware container.