My brother and I are in the early stages of development and design for a game we are making together. He's the genius artist and I'm the programmer guy. Everything in-between we share, including map making. There's an excellent free tool called Tiled that can be used to make 2D maps. It supports layering, automapping, animations, and even collision boundaries. In short, it's a fantastic tool for creating 2D maps.
Unity is the game engine we are using. It's very popular, full featured, has an excellent store for assets/plugins, and, most important of all, it's free for small developers. We wanted to see if we could use Tiled maps in our Unity project and I was completely willing to write a script to load an exported Tiled map into our project. Turns out, there is already a fantastic free tool (you can make a donation to support the author) for doing just this. SuperTiled2Unity is a plugin for Unity that allows you to just drag and drop your Tiled map file and textures into the project assets folder and they get automagically imported.
I was able to easily import our test map and then add it to a scene. If you update the map file, the changes are automatically imported into Unity. I still need to explore how the animations and collision boundaries work, but it seems like a really promising tool that will exponentially reduce our development time.