"Freddie's Dead" from the soundtrack to Superfly is a great minor key funk groove. Curtis and the boys start in C#min, move it up a half-step to Dmin completely unexpectedly somewhere in the middle, and then bring it BACK DOWN to C#min again. It catches you off guard every time, and it's a testament to Mr. Mayfield's vocal control that he can adjust so quickly, in addition to have the slickest voice ever.
And for what it's worth, I'll bet that this song is what gave Flea his inspiration for the bass line to "If You Have To Ask." Bass players, listen for the triplet-sixteenths in the breakdown.