7digital United Kingdom | High quality DRM-free MP3 music downloads(UK) have free MP3s regularly, usually samples of new artists.
for creating ringtones from your own music,
Audacity is hard to beat.
But you'll need the
LAME encoder plugin to export in MP3 format.
There is also a huge range of effects and sound processing plugins available, A selection of which are included in the Audacity download.