Here's a site that I share with my students. It's got a LOT of good sounding backing tracks. This allows them to hear their experiments, in context. It's also good for making scale practices less boring.

http://www.guitarbt.com/index.php?page=dl_list

Some of these Backing Tracks sound really good!

For you guys with the BR-600s, you could load these into the BOSS recorders, and use them as practice materials. Good for trying out different tones. As you can hear your playing in a "band" context.