As of, well, today, the alpha version of Sega Dreamcast emulator Reicast is available for Android. It's essentially an Android-based version of Nulldce.
Quick warning: the developer of Reicast reckons that you'll need to have at least a Cortex-A9 dual-core 1GHz+ processor in your Android device to run Reicast properly.
You'll also need the Dreamcast BIOS for the Reicast emulator to work. Oh, and to read the following instructions:
"Put [the BIOS] on /sdcard/dc/data/dc_boot.bin. The Dreamcast flash should be on /sdcard/dc/data/dc_flash.bin. You should dump these files from your Dreamcast and the games from the original gdroms (gdi or chd format)."
There are more in-depth tutorials on the internet for using Reicast, though, if you need them.
Given this is an alpha version of Reicast, you might obviously come across a few bugs. Otherwise, you should have no problem running the likes of Sonic Adventure, Crazy Taxi, Soul Calibur, Resident Evil Code: Veronica, and more.
Reicast even works on the Ouya, by the way. So, if you have one to hand, you download the .apk file and get it running on a big screen.
You can download Reicast for free on Google Play [download] right now.DroidGamers