This hint is similar to "Smart iTunes Playlist use for small iPods" but requires less work. Now that my music collection has exceeded my 5 GB iPod, I can no longer auto-sync my entire library. I don't really want to manually update the songs and playlists or uncheck all the songs I don't want updated. My solution is to create a Smart Playlist with the conditions Genre is not Spoken Word and Kind does not contain stream (You can choose whatever conditions make sense for you).
Next -- this is the key part -- limit the playlist to 4,500 MB (for a 5 GB iPod) selected by "most recently added." This will ensure that the playlist contains only as much as your iPod can hold and always includes your most recent additions. You could also select by highest rating, most often played, etc. Name the playlist "iPod Selection." Then in iPod Preferences, select "Automatically update selected playlists only" and make sure that iPod Selection is checked. To open iPod Preferences, select your iPod in the source list and look for a button in the lower right corner of the iTunes window. Now your iPod will be automatically updated with as many of your newest songs that it can hold -- and you won't have to think about it!