Check the icons to find out what kind of tracks they have. Most of them also offer to download the tracks as .gpx
Database with more than 50,000 tracks from basically everywhere.
Nice database with more than 50,000 Tracks from all over the world
Biggest database (we know of) with more than 90,000 tracks of more than 100 countries.
Database with more than 2,500 MTB Trails (focus on the US and Canada).