ActiveState has released Komodo IDE 4. Perhaps more interesting, if you're not already a Komodo user, is the release of Komodo Edit, which is very similar to the old Komodo IDE Personal edition, only instead of costing around $30, Komodo Edit is free. The mental difference between "free" and "$30" is much more than the relatively small amount of money; it will be interesting to see what happens in the IDE space now.
After a brief evaluation I would say Edit is perhaps the strongest contender for "best free python IDE." The only serious alternative is PyDev, which on its Eclipse foundation provides features like svn integration that Edit doesn't. PyDev also includes a debugger, another feature ActiveState would like to see you upgrade to the full IDE for. But Komodo is stronger in other areas such as call tips and, well, not being based on Eclipse. I also think its code completion is better, although this impression is preliminary.
It's also worth noting that so far, Edit doesn't sport the "Non-commercial and educational use only" restrictions that Komodo Personal had.