How to handle miniatures on a forum-based game?

Question

When running a web forum game of an RPG that requires miniatures (such as D&D 4e), what's the most elegant way to handle a combat grid?

In particular:

• Players should be able to change the map without DM present (employing group initiative and "players roll all the dice" rules, so the game doesn't lag waiting for any one player or the GM)
• It doesn't matter whether the graphics are fancy or low-tech, as long as it's a combat grid of some sort (as opposed to minis-free alternative)

Answer 1

There's always the very low-tech solution of ASCII text graphics. It's not terribly efficient, but it's doable.

Sample 10' wide intersection in 5' grids

+   +   +   +   +   +   +   +   +
            |     T |        
+   +   +   +   +   +   +   +   +
            |       |        
+---+---+---+   +   +---+---+---+
     Pl4 Pl1
+   +   +   +   +   +   +   +   +
     Pl3 Pl2 
+---+---+---+   +   +---+---+---+
            | O2 O1 |        
+   +   +   +   +   +   +   +   +
            |       |        
+   +   +   +   +   +   +   +   +
            |       |        

Every player cuts and pastes the map, editing it for their turn. So, after the Troll "T"'s turn:

+   +   +   +   +   +   +   +   +
            |       |        
+   +   +   +   +   +   +   +   +
            |       |        
+---+---+---+   +   +---+---+---+
     Pl4 Pl1 T
+   +   +   +   +   +   +   +   +
     Pl3 Pl2 
+---+---+---+   +   +---+---+---+
            | O2 O1 |        
+   +   +   +   +   +   +   +   +
            |       |        
+   +   +   +   +   +   +   +   +
            |       |        

Answer 2

If it doesn't have to be in a forum, I've always found a Google Spreadsheet the easiest way. I've also seen a few good online map applications which use a token overlay system. I unfortunately cannot remember the names of any of them, and my googlefu is failing me.