IndabaMusic is a great place to meet other musicians and collaborate online. Indaba has an innovative flash powered mixing console, which is cool since you can download someones track, load it into your favorite Digital Audio Workstation(DAW) and cut your tracks. Then when finished upload said tracks to Indaba, load them into the flash console and mix away.
They have an active online community – and your likely to find musicians who play all kinds of different instruments and musical styles.
My IndabaMusic profile is here: