While I've been a happy iPod owner since the very first 5 GB model, I realize that we live in a world with plenty of other devices that can play music. Fortunately, a company by the name of "utsire" realizes this as well and has created Thrupp, a handy utility for sending your iTunes music (sans iTMS purchases) to virtually any other MP3 player that can be mounted as a drive in the Finder, including music phones.
Thrupp is smart too, as it not only can convert AAC songs to MP3 for your device on the fly in the background while you work, it can also display all file sizes and free space, letting you keep an eye on exactly how much space each song is going to take up. Now I haven't grabbed a copy since I don't have any music playing devices besides an iPod, but Thrupp's screenshot looks like it can display your entire iTunes music library as well as your playlists, making it easy to track down just the songs and albums you want.
Overall this looks like a good app for all those non-iPod devices out there. A demo is available, and a full license is $14.95.