Well, there are plenty of options - I use an old PDA and keep my MP3 files on large capacity SD cards - works fine for me; but there are plenty of different models out there - my son & DIL swear by their iPods and iTunes (check out the site to see if their format suits you & your wife); also, the computer mags review these products often - look at
THIS LINK for a listing of some top 'current' choices, reviews and recommendations - good luck in your choice!