Shuffle Medley DJ is the best way to Explore the music.
This app will automatically crossfade the "song in your iPhone" and the "Top Songs Trend".
The newest feature of this app is that each song will play small amount of time which will let you enjoy large amount of music with a very excited moment.
If you choose to listen the "Top 200 Songs Trend", you will find out how fast you can seize the trend and spreading your knowledge of various songs and artist.
The playing duration and the crossfade time can be changed on the setting too.
Its free, give it a try!