Check out my PBP Post
#22 and the attached thumbnail, and then a few posts later at
#32. (You can follow the whole combat in a 10 post series- 6th level PCs against a Troll and a pair of Krenshar.
I use a layered graphic system I made in Paint Shop Pro. The bottom layer is blank white. The next layer is 'terrain' and I can just change it to whatever and save it to whatever. It could be a dungeon room, an outdoor scene, or whatever I like. The next layer is a number-letter grid. Players can say what square they go to. Like "I run to H9".
Then the top layer is the "miniatures" just disc-shaped graphic counters.
I manipulate the map by going to the miniature layer, using the lasso tool, and moving it on the grid. Because it uses layers, it doesn't disturb anything underneath. If I need "destructible terrain", I can do that too - just by jumping to the terrain layer.
When it's done, I 'flatten' the graphic (to merge all of the layers and reduced the kb of the graphic) and 'save-as' with the name and the round number of the battle (this naming convention also organizes the archive of the battle in order). Then I just upload it.
So we can doo all of the threatened squares, AoO stuff just fine. The only issue I have is I only post the map once per combat. So if a guy says "I run to H9 and cast my spell" but I had the troll move first in initiative, and he happens to have moved right into the threat zone of that square, I'll let the guy rethink where he wants to go.