I don't know how good or bad this game is but it's pretty cheap. Next cheapest is £14.95 @ Mymemory.
Def Jam Rapstar is the first music game fully dedicated to Hip Hop
With over 40 songs spanning the history of Hip Hop, Def Jam Rapstar offers a diverse track list with some of the biggest songs in Hip Hop from all music labels
Unlike most other microphone-based games, Def Jam Rapstar features custom, proprietary voice recognition technology that judges lyrical accuracy
Utilizing the Xbox Live Vision camera, Def Jam Rapstar allows you to create a video of the performance starring yourself, edit, and then upload to http://www.defjamrapstar.com
Freestyle mode allows MCs in the making to kick your own lyrics over well-known producer?s beats, offering a chance to show and prove that you have what it takes