I've just completed a first cut at a web based map generator that might be helpful. It's not an "editor" that lets you fiddle with the details of individual planets, but it will let you specify start positions, how many star systems are where, and gives you some control over system size, planet quality, etc.
You can bash out a fairly customized map in about two minutes, so if you're going to edit by hand, it will at least get a lot of the tedious work out of the way for you.
http://theharms.org/cgi-bin/gc2/webmap.rb