Seriously. Ask THEM what they would like to see in a computer lab.
School for me, plainly put, sucked. I did poorly because I never had any reason or desire to motivate or engage myself. Environment is important, as someone else said, but it also needs to be a place that doesn't feel forced. Put meme posters (that are safe for school) on the wall. Interesting trivia. Places students can go whenever they want to learn (slashdot!).
Encourage them to learn and understand. Bring in computer parts for display. Show them what real world internet is like. Discuss and have information about the difference between over-security, network security, theatrical security, and how that ties in with laws.
I think the ideal computer room should have all the evidence of what I would want to impress upon my own children about computers and the internet.