download torrents of mixtapes based on genres you like.
for instance; if you like electronic/house/top40mashups go with kapslap, 3lau, victor niglio, etc. they have tons of free albums of good mashups and tracks.
rap you'll find tons of mixtapes, hip hop, pop, chill, etc. but not all genres will have multi-artist mixtapes.
get artists' entire discographies too. it's really cool to be able to listen to an entire album from start to finish.