I'm going to parrot a bit the above answers in regards to MapTools, but add a bit more to it, since I think the question is slightly incorrect in regards to the app.
First off, MapTool is a part of a larger RPTools suite, but none of the other tools are required. I'd suggest TokenTool at a minimum, since making token graphics is dead simple using it. (Drag image onto TokenTool, zoom in/out, position, select a border, then drag the token from the upper-right onto Maptool and drop it onto the map -- done; no need for saving/loading "in between" steps.)
MapTool itself is very flexible in how much you want to use it for. Just want quick hand-drawn maps and tokens to show position? Very easy to do. (Obviously you are looking for more.) On the other hand, the macro gods that post their works on the forums have made several very nice "framework" packages to handle most of the popular games. Some handle things better than others, but the community rocks when it comes to questions and support. It's one of the few forums I check regularly because of the community there alone.
Lastly, making maps in MapTool is very easy, even if you want to get detailed. Very simple tools allow for a quick learning of how to do things, but even better if you are into dungeons and the like, is Torstan's tile-set. Simply put, they are walls-tiles that snap to the grid and allow making a dungeon map very, very fast. Drop on objects and items for look and feel, and you can have a nice looking map in no time.
I've been running games using MapTool for a long while now and I can't imagine -not- using it. Best price and best support for the price. ;) I've looked at other VTTs, but it is always the cost that gets me; I'm willing to pay for decent software, but I am not willing to force my players to do so just so they can play in my game.