I wanted to do this, so I started JamBase (http://www.jambase.com)

Essentially, you can register for a MyJamBase account (http://my.jambase.com), enter a list of the bands you like now and it will connect you with other people who like similar bands and help you broaden your musical horizons.

It won’t do it for you (yet), but we’re working on tools to make it much easier.

Let me know what you think.