If you're a Spotify Premium subscriber, you can now move beyond simple crossfades thanks to the DJ Mixer for Spotify iPad app. In order to use it, you have to download songs from your existing playlists, which also lets you use it offline. As with other such apps, you get two virtual decks and can set loops, add cue points, and change the tempo for your mixes, among other features. We gave it a spin ourselves and found it to be easy to use in relation to other DJ apps, despite any lack of talent. You can grab it for free at the iTunes link below, since Spotify prohibits apps that use its API to charge money. With 20 million songs to choose from,
Update: The app has been removed from the App Store at Spotify's request, which apparently felt it violated its terms of service. A representative from the publisher, Musicsoft Arts, made the following statement:
The App was removed from the App Store due to Spotify's request. Spotify claims that some features breach their API terms of service. We have designed the App to fully conform with their T&Cs. We are talking with Spotify and hope to be able to put the App back in the App Store once this issue is resolved. There's clearly a demand for the App and I believe it can deliver a great experience for Spotify users while complying with Spotify terms of service for 3rd party mobile Apps.