Of all the apps I've downloaded for my new Android Nexus S phone, this is the one that I value the most. This allows you to fully manipulate the sound quality from your headphone jack, your speaker, and your bluetooth audio connection. I find it quite odd that Google itself hasn't put these tools into the system natively.

Make your Android sound come alive!

Now, I just wish that there was a similar app for adjusting screen color and gamma!