The Galaxy Editor is not out yet however it is still possible to start working on maps. I will show you different projects that have already been started by the Mapster community.
How To - Überlisk by Hati
We just opened a new Tutorial Forum where you can learn and share knowledge about various aspects of the game. The first posted one will hopefully help you start editing maps by making an Überlisk as shown in the Blizzcon movies. Hati released a detailed overview of the required files and how he achieved this. Here is a preview of what you will get at the end.
3D View by NVidia
Iggyhopper makes us a demonstration of Stereoscopic 3D version of Starcraft II using NVidia latest graphical cards. I can't test this as I don't have the required glasses but I'm pretty sure it is going to get a better immersion feeling.
Yeah the NVIDIA "rating" is good, not excellent, with some notes about some objects not rendering at the correct depth.
it doesn't work THAT well (last i tried) as in 3D things like the selection rectangle, cursor and user interface elements and more annoyingly unit health bars all show up floating on top of everything basically sticking out in your face making the game kinda unplayable, easy enough for Blizzard to fix or workaround if they so desire to, not sure how they could do a cursor that isnt annoying though :-/
Also naturally its only worth a damn if you have a 3D capable display as using red/blue anaglyph glasses isnt really an option as it just looks awful :-)