So I'm particularly interested in finding map sources that can be used as combat aides for d20-style games.  Systems/sources that can be used for tactical combat, as well as area and regional maps for simple orientation/information.  Ease of use and inexpensiveness of cost are good bonuses, as well as the ability for players to possibly manipulate the maps a little (such as moving tokens representing their characters in combat).  Ideally, I'm looking for something that I could link to in my games here on RPOL.

do a search for online map client

I know there is one out there that saves a map with data on there sight that you can link to for online games. That way you can edit it and players can see it with out having do to ACL stuffs.

Dramascape makes a product line for combat maps and such.  You get printable versions as well as VTT versions.  Their maps also cover several genres as well.  Hope this helps.

Putting map images and token images on google images gets the job done nicely.

Everyone can move stuff around, and there's a change history.

There's one which I seem to recall is called Pyromancer (or something along those lines) where players can move stuff around and save it.
There's another one I like called MapTools which is a downloadable thingy where you can build maps (on a hex or square grid) but you can't have players update it "live" unless you use it via a server, otherwise you have to do all the editing.
But they're both free :).

In reply to kouk (msg # 4):

That one comes in handy! I've also used google spreadsheets for strategy gaming where you have lots of resources to manipulate too, it's also helpful that you can share those with others easily.