Yesterday I found something very neat on StumbleUpon: musicovery. This is an online radio service in which you configure the playlist by setting your preferred music genres , the mood on 2 axes: Calm-Energetic and Positive-Dark, a timeframe and flags for hit song and new song. Based on these choices, the service compiles a playlist for you which it follows. I must say that I was amazed at how accurate the generated playlist reflected my input. The best thing is that this service is for free in LO-FI version and the HI-FI version costs only about 10 euros/year.