A while back we mentioned some ways to develop a meta-data tagging system for your files to be used together with, or even as a replacement for, standard hierarchical organization. TagBot is another tool designed to help make tagging easy. Basically it allows you to tag files either by dragging and dropping them onto the appropriate tag in a "Tag Palette" or by selecting the tag from a contextual menu. The tags themselves are added to the Spotlight comments of the files for searching, etc. Nick Santilli over at The Apple Blog has a nice little screencast that gives a good sense of how it works.
TagBot is $20 and a demo (limited to six tags) is available for download.