Here's a bright and sparkly girly retro-inspired theme. :)
http://atypicalife.net/blog/free-wordpress-themes-for-download/
It's widgetized, works in MU, and has an options page where users can change the font style and size, plus they can switch from pink to blue to green color options. Screenshot shows all three. The content area is flexible while the sidbears on the right are fixed.
I used it for quite a while on my own blog.