If you're looking for something a little bit more intuitive when it comes to building playlists for iTunes and your iPod then you might be impressed with that beaTunes can do.
beaTunes works by analyzing the songs in your existing iTunes library and then correcting discrepancies such as double entries, incorrectly labeled songs and artists, misplaced genres and much more. When you run the library inspector on startup, it will display the errors or problems it has found and then ask you how many of them you'd like to correct. In the trial version, you can't make any corrections but you can see what's wrong with your collection.
beaTunes can also auto organize playlists by such things as genre, rating and even beats per minute. It could be regarded as a virtual DJ although as with all apps like these, some of the suggestions and mixes it will make will inevitably be a bit dodgy. beaTunes goes beyond what you've got installed on your Mac though, and interacts with both the iTunes store and Amazon database. This allows you to discover albums related to your music that you might not have heard or just follow the Amazon charts. The Amazon charts take a little while to load but you're presented with a thumbnail of each album currently in it plus you can divide the charts into genres too. beaTunes is a nice little application that could help clean up your iTunes collection and introduce you to new music.