Reicast is a Dreamcast emulator for Android that will run on phones, tablets and set-top devices such as the Ouya. Although its an Alpha it appears to run quite well on my 2 year old Galaxy Nexus phone. Sound works and games run at full speed with the ability to save.
The two games i have tried appear to have graphical glitches (Sonic Adventure 1 and 2), however from looking at the screenshots on Google Play that's not the case for all devices.
Well worth checking out if you liked the Dreamcast anyway!
Google Play Link: Reicast