Mixed in Key has teamed up with Allen & Heath to release Mixed in Key 4.0 for Windows and Mac OS X. I'm not sure how this one flew under my radar for the previous 3 versions, but it sounds like something that would be useful not only to DJ's, but indeed to anyone who uses loops or sampled musical phrases in their music. From the website:
"Mixed In Key is software created for the world's best DJs. With its user-friendly design and trusted technology, Mixed In Key makes harmonic mixing easy.
Mixed In Key takes your mixing to the next level by showing which songs you can mix together without a key clash. It works with all CD decks, Ableton Live, Traktor, Serato Scratch Live, and all other mixing software and hardware. Your DJ sets will always sound smooth and professional. "