What's a good skybox for this game I'm working on?

Hey there!

I was wondering what kind of skybox I could use in my game since the background right now is just black. Some recent screenshots:

1, 2, 3

You can find more screenshots on Flickr here (more recent on bottom), and here's a video (slightly old).

The game's supposed to be set in a lab but I'm not sure how that works anyway with the kind of levels I come up with, hehe.