By request, here is a step by step of how I made this week's extra-dimensional Mystery Map. Note, this tutorial requires Photoshop (I'm using CS4, but any version since 7 should work).
I used the Chaos Circle brush set available from Qbrushes.com
Step 1. Splatter some random watercolor onto a piece of white watercolor paper:
Step 2. Scan into Photoshop
Step 3. Invert image (yeah, pretty awesome huh? this is where the "magic" happens!)
Step 4. Load Chaos Circles brush set and on a layer set for screen make some random brush stokes with Chaos Circles (or not so random if you have specific ideas of placement). What screen does is show the image only in the light areas and not in the dark. You could just play with transparency.
Step 5. Using Symbol font (which makes Greek text - very cool looking!) label various circles with English words. For example I used: Pandemonium, Abyss, and Element
Step 6. Do a Google image search for Stars and find a cool hi-rez image of stars and set that on a layer Set for "Lighter". (or you can splatter some ink on a page and scan that in, then invert to get white dots on black, which is what I did)
You now have a really cool extra-dimensional map. For additional coolness you could make dotted lines connected various "spheres" or overlay a grid.