libGDX[1][2] (it's not an engine) is a great cross-platform Java library that allows you target the desktop (Win/Mac/Linux/etc), Android, HTML5 (through GWT), and now iOS all with the same codebase, built on standards like OpenGL ES/WebGL.

Mario Zechner (the main guy behind libGDX) wrote an excellent book[3] last year on Android gamedev that has you start from the basics up to creating your own game engine and games.

[1] http://code.google.com/p/libgdx/

[2] https://github.com/libgdx/libgdx

[3] http://www.amazon.com/gp/product/1430230428/ref=as_li_ss_tl?...