nice one for the replies so far
stuff i've found:
some bootlegged multitracks of sessions from people like stevie wonder, the beatles, marvin gaye and queen. listening to the individual tracks from bohemian rhapsody is pretty enlightening. freddie's vocals soloed is nowt short of awe inspiring, he's on some top shelf opera level shit. my fave is probably the doobie brothers - long train running, that one is just bad ass. google "multitrack masters"
there is a pack of motown acapellas out there
and then for stuff more specific to dance music there is the
defected acapellas releases which i managed to find on a blog in mp3... i used blogsearch to find those. there are 9 cds in the set, some of them are way to camp for me, but theres a few bits in there well worth checkin. i really dig the one osunlade used for momma's groove on vol. 9. they're only 5 quid so might be worth investing in.
keep the suggestions coming
oh yeah, i should add that i have been through around 10 'dance vocal' sample cds from various sample houses and for the most part the stuff on those is, to put it bluntly, cringeworthy. there are always a couple of decent sounding oooohs or ahhhhhs but most of the time when they try to be soulful they just don't cut it. also, i read on an audio production forum the other day that a lot of garage was made with sped up r'n'b sample cds which is one area i've yet to check. they might be worth investigating
cheers