I'm currently in the process of building a summer (prototype) project to try out some ideas I've been toying with for a few months now. The idea is cross mobile platform applicable, but since I own a HTC Touch Pro 2 with WM6.5, I might as well try it out on that.

However, the current UI available for Windows Mobile by default is horribly looking, and to make the prototype a bit more appealing I'm looking for a UI toolkit that offers a bit more modern look. I tried googling for a bit, and found mostly commercial toolkits, which is a bit too much for a prototype that might never be commercially exploited.

Toolmaker

You should check out the Sense Interface SDK on XDA. It replicates the look and feel of TouchFLO/Sense very closely.