I've always liked Team Viewer for quick and easy remote control of Macs and PCs. Today, they've pushed out an updated Mac client that has fixed a few small quirks introduced when Lion arrived.
One thing to note. The Mac version of Team Viewer doesn't alert you that there is a new version, and it does not have a 'check for update' option, so just get yourself to the Team Viewer website to download the free update.
Team Viewer also has clients for the iPad and iPhone, making it a pretty complete free solution if you are using it in a non-commercial way.