I recommend you the free Mappy editor:http://www.geocities.com/SiliconValley/Vista/7336/robmpy.htm
This editor is not very user friendly but very powerfull! The author provides a good doc and a tutorial on using it.
Also multiple level loaders are provided but the Java version is badly implemented and not really performant but if you want I can provide you a copy of my own mappy loader (based on the author's one) which performs well and is a bit more object oriented (other enhancements still need to be done in this field).
I'm using it in my 2D side scrolling game and to date it performs very well!