While on this subject I wanted to point out that I recently got some interesting covers off ebay.

The 20 long covers have 3 lock knobs that actually hold it on quite nice.

They also have a very fine mesh on the screen, so if you have any of Kyle's roaches, they would be a great cover.

The 10 gallon covers set down IN the ridge around the top, and have 4 small knobs that slide locks up under the lip.

The 10 gallon covers also have 2 round ports so they can have hamster tunnels added. (for feeder mice or pets)

There is also a metal recess for a UV lamp for use with lizards. (Or any fluorescent fixture for light)

And the best part, cheaper than less interesting covers at the store.