Rdio is a new streaming music service, available on the web, desktop, or your BlackBerry. You can add as many songs/albums to your online collection, accessible from any of these platforms. Rdio also supports playlists, and people (similar to Apple's Ping). Possibly the coolest feature is the ability to resume a song/album/playlist from where you left off last, when transitioning from desktop to mobile, or vice versa. Their collection of music seems very complete, and every song I searched for was found, and available for play. Rdio streams over WiFi, 3G and EDGE, comes with a 3 day free trial, and is completely ad free.
Overall, I think $4.99 per month is a fair price for those who listen to a lot of music, and may not have the space on their device to store enormous amounts of music. It brings unlimited music to you, wherever you are, even if you don't have a cellular signal (available music caching). However, this probably won't entice the casual listener, or those who listen to free streaming radio services like Slacker, and Pandora. But, it is another choice. It is now compatible with the Bold, Tour, Curve 8500, and Storm devices.