First of all a great new 2D editor, Overlap2D, has been released under the Apache2 license:
Contrary to other popular 2D editors (for example tiled or DAME), it is not tile based, has a modern renderer and also comes with a nice GUI editor. It currently exports to a standard JSON file and has a libGDX runtime.
Godot 1.1 BETA
Really awesome are also the latest developments of the (often described as the open-source Unity) Godot engine which you can now easily try. For me the coolest new features are the new dynamic lights (shown here in the also new isometric game sample):This of course requires a bit more than simple 2D sprites ;) If you want to create cool 2D normal-maps, this should give you an simple way to create them.
Also very nice is the now working graphical/node-based shader editor:
If this has raised your interest in developing a game with Godot, check out this nice series of tutorials or these. It's script language is a simplified version of python, so most beginning coders should feel right at home. Also check out this cool video of a mobile game made with Godot, if you still need convincing ;)