Acapellas in G flat or F sharp!!

Mixed In Key is awesome software ideal for this sort of thing.
It will tell you simply which songs are compatible with each other using the ‘camelot key’ method.

Changing the key of an acapella can be done but often makes it sound a little strange.
Most DAW’s have features which will do this, I use Logic, and find the easiest way is to create an apple loop from the pella.

If you are creating the song its probably easier to make the song match the pella rather than the other way round tho.

We actually hold Mixed In Key data for the entire collection (and lots of other cool stuff).. I just need to see my developer to bring this to life from the test site to the live site

there are also programms that can figure out the key of an audio file! I’m not sur if I’m allowed to name them(because of advertising)

another thing to consider is that you don’t always have to remix a vocal in the same key as the original song: you can reharmonize! use the same melody but put different chords underneath it. if your track is in F# minor, for example, you might try fitting a melody in A major on top of it. this is most easily accomplished with simple melodies, and it helps to know some music theory and/or have a good ear, but it’s something to experiment with.

^^ this guy here^^ :p but yeah, a pitch shifter would do the job and could sound cool too…..