Radiologik DJ is the DJ live assistant specifically built for the needs of radio but very useful for all DJing needs, with the exception of club mix features. It features 3 main players and one library player, all with selectable individual audio outputs, detailed time calculations, a lot of fast and smooth iTunes integration, and Nicecast artist and title publishing. It is complemented by a free separate scheduler for full station automation.
The published price is that of Radiologik DJ Personal, though the app has a variety of editions available for purchase. Compare the differences and view the prices of each edition here.