I'm not aware of anything that will do it to the beat of the ringtone.
An app called noled will put led-like notifications up on the screen on new sms etc. i also believe it now has the led buttons as an option.
I however am rooted, so i have installed back light notification (bln) so don't use noled. Both consume battery, noled even more so, so it's worth bearing this in mind.

 

S2 doesn't have a notification LED. You can get the soft buttons to illuminate but you need root and a rom that supports bln. Alternative is to download an app called noled from the market which illuminated a notification on the screen.

 

I think adamantell means the LED flash

 

You might be able to do something with Tasker and a flashlight app.

 

You may also want to look into the cost of spare batteries and replacing the LED flash as well.

 

Go here, and follow my instructions. It wont flash the 'flash LED' to the music but you'll have the soft keys notification, which is pretty cool.