For contacts, I use the <a href="http://www.apple.com/applescript/ipod/" target="_blank">Address Book to iPod</a> AppleScript, which is really handy for keeping all of your information in one simple program.
For file management and MP3 transfer, <a href="http://www.versiontracker.com/moreinfo.fcgi?id=14715&db=mac" target="_blank">PodUtil</a>.