There are a number of options for generating the data. I second Markr's suggestion to use Inkscape or some other similar program to create the level data. You could then process the SVG to something more game specific through a script or XSLT . You could choose to store such data in a number of formats such as XML or JSON. There is even a commercial solution called Corona for the SVG approach.
You could alternatively develop a level editor using C#, PySide, Qt, Java, ect. This route would be significantly more time consuming then using an existing vector graphics program though.