Calvin Harris has recently made a bunch of vocal stems available for download on Soundcloud: https://soundcloud.com/calvinharris
If you're doing remixes or just learning from the master, his occasional stem releases are golden. I was working on a remix for Summer last year and the only stem available was from a dodgy DJ site that was mostly unusable, now you can get the real thing straight from the source.
Calvin Harris rocks!
N.B. Calvin Harris watermarks his stems so make sure you get permission before publishing a remix.