http://www.cambridge-mt.com/ms-mtk.htm#UnicornRodeo_Maybe
A list of multitrack projects which can be freely downloaded for mixing practice purposes. All these projects are presented as ZIP archives containing uncompressed WAV files (24-bit or 16-bit resolution and 44.1kHz sample rate). For maximum mixdown flexibility, the contributors have made every effort to provide audio 'raw', in other words without additional effects or processing (beyond treatments printed during tracking/editing).