Many MP3 players that require media player or iTunes need them to create a
database in addition to the music files themselves. Both Amarok and
Rhythmbox and perhaps Banshee can do this. I don't do Mono so can't say :).

They support MTP devices which connects to many such players including
iPods. My son has been through many players and likes Cowon and Sansa Fuze.
I have a Philips 8 GoGear GB that sucks. It works well enough but does not
support ogg, or flac. Fortunately I got it refurbished for a song. I would
not buy another player if it did not play these formats. I get most podcasts
in ogg format and like flac as a lossy format.