I have one, I should know. I'm looking into replacing it before this summer gets any further along. I'd love to get the Visteon (Ford) version of the PhatBox by PhatNoise but they seem to be taking their sweet ass time getting the unit out. Soon, soon, soon. It's always soon... I really want to go back to my old stock head unit. Not only does it look good in my car, it also features automatic volume control which I really miss. Why must most aftermarket head units look so flashy and ugly? Oh yes, I'm never buying another Aiwa product again.
Check out the JVC KD-SX980. It has resume. Read the user write-ups at [link|http://pub56.ezboard.com/bhighwaymp3|http://pub56.ezboard.com/bhighwaymp3].
If you're looking at replacing the Aiwa you should look into the Kenwood KHD-CX910 Music Keg which really is the PhatBox. You'll need to buy a Kenwood head unit for it.
There is also the Alpine CHA-S634 which is a 6-disc changer that supports MP3s. Again you'll need an Alpine head unit for it.