Jam11 is a new app (currently in beta) that allows you to stream your iTunes library to your BlackBerry smartphone. It also streams over 40,000 SHOUTcast internet radio stations, from around the globe. During my testing, I have personally experienced lightning fast streaming over 3G and Wifi. It is also nice that the app will also stream over sub-3G connections, a feature that a lot of apps don't support.
Jam11 is a great app for those who have massive music collections and do not have the space on their device to hold it all. You can download it at BlackBerry App World free of charge in the beta section. It supports only non-touchscreen devices at the moment, but hopefully will add touchscreen devices soon.