Audubon Birds by Green Mountain Digital. This review describes the Android version.
I was in the market for a inexpensive Android bird watching application. The highly touted Sibley guide cost $20. Other programs seemed cheap and shallow by comparison. I finally chose a name I knew from my paperware guides — Audubon — which cost about $4.
This guide offers an in depth view of North American birds as far south as Mexico. The data base is a space hog: you can either access it via the web (which can take time when InterNet traffic is heavy) or you can download it to your cell phone/tablet. The developers suggest putting the app and its database onto your SD card but with my Google Nexus 10 there is plenty of room.