Funny, no one (I think) has mentioned a disco ball. I love mine - always gets the "that's so cool" comment and is great to have lights in motion in the room. Adds more life.
Also consider moon flowers - go to www.musiciansfriend.com and look nder DJ lighting. The $60 moonflower light by Chauvet is great. While there, look for a lazer light if you have the money - about $300 will have tiny pins of green lazers dancing around your room too.