I've been meaning to run a sandbox campaign for a while now and tonight I sat down for a little while with the free version of Hexographer and The Welsh Piper's campaign design tutorial. Here's what I have to show for about two hours of thoroughly enjoyable work:
On the left we have a scale of 5 miles per numbered hex, on the right we have a scale of 1 mile per numbered hex. The red tint on the left shows what I zoomed in on to get the right, so the big central hex on the right map is hex 05.05 from the left map.
Did I end up with a particularly cool map? No. Is it good enough for a trial-balloon sandbox? I am pretty sure it is!
Note that I tried to follow the tutorial to the letter (yes I actually rolled dice for the left map), so I guess this also shows that Erin's method produces fairly decent outcomes. (Of course his method is not an exact algorithm, you do have to tweak things here and there to make it work.)
Next I'll have to populate the maps. Erin has another tutorial for that, but as far as I can tell his method will produce too few adventuring sites for my taste. So I'll probably just populate manually, or maybe by stealing ideas from other sandboxes I have access to. We'll see.