pth files are your friend
Why is it that many Python packages insist on littering your site-packages folder? It's not very hard to make a setup.py that has its own little microcosm referenced by a pth file, and it makes the user's life so much better. See Numeric, PIL, or PyObjC for decent examples.
Bonus: the user can easily uninstall, cleanly upgrade, or even move the package to an alternate location simply by moving it and changing the path in the pth.
Update: It looks like this is done with the extra_path argument to setup(...). I would've mentioned it, but I didn't realize that it wasn't documented outside of the source, mailing lists, and files in an old CVS attic!