It depends on a few things... if you are just trying to organzie them on your HD and do not need to synch them up to a MP3 players.. then any of the software will work. Itunes, musicmatch, winamp, etc.. all do a fair job or finding your mp3 and allowing you to sort and rename them as needed.

If you want a really good piece of software that will also synch effortlessly to mp3 players, I highly recommend the free mediamonkey.. it is by the far the most feature rich of the mp3 software... of course, it really helps to have ID3 tagged mp3's to start with. If all your mp3's are from ripped CD's.. then you should be all set. If they are from.. shall we say.. alternate sources? then... you will have some work to do to edit your tags. There are freeDB tools in MM that allow you to attempt to fill these in based on the song.. Good Luck - it is a daunting task - I have over 30GB of music - most of it is organized and easily found by genre, artist, etc and I store the whole shebang on a portable MP3 player.. it goes with me and my music is available anywhere. When I am home, I just plug it into the PC and MM automatically synchs if needed and I can play my playlists or just listed to the songs..!