I did a search today on a carrier portal for Bruce Springsteen.

The results were:

Games and Applications: Hungry Puppy 3D (How do they know I'm starving my iPlay puppy?)
Ringtones [nothing specific]
Ringback Tones [nothing specific - offered similar music]

At the same time they recommended:

Scuba Solitaire
Midnight Pool
Virtua Tennis

???

I tried it again with the search terms "U2."

This worked and they sent me links to some ring tones and ringback tones. Lots of clicks to buy, etc. but this was fairly well integrated with the mobile content portal. Liked it.

They recommended:

Over my head (cable car)
Lightening crashes
Afterglow

???

Search worked well - not sold on the recommendation engines yet.