I use Django. For the most part it does the heavy lifting and then gets out of my way and lets me code. Another large factor I really like is the peace of mind knowing that it actually works in production environments and isn't impossible to scale. Also, their documentation rocks.
The only other one I've really checked out is web.py. It has a much more raw feel to it. I'd probably switch to it if for some reason Django started getting in my way a lot.