Before Arlo was born, I obsessed mildly over finding or making a brilliant, stylish, intellectually stimulating, and affordable mobile to hang over his crib. I didn't really succeed, though we did end up receiving a very sweet, Scandinavian-simple, wooden butterfly mobile in primary colors from my sister and her family in Denmark--which not only graced Arlo's crib airspace, but also did double duty as our Christmas tree topper (suspended from the ceiling over our plastic Salvation Army tree) last year.
I digress. My point is, looky here! http://www.cookiemag.com/gear/products/2006/09/mobiles