Run actions after the last one is complete

I would like to have a wait for action to complete option.
That way I can drag my dmg's over to mye sort folder. They will get mounted and moved to trash. Now the just get moved, not mounted.

What action are you using to mount the dmgs? In general, actions do not run until the last one completes. There are a couple exceptions. The "Open file" action (maybe that's what's your using?) may "complete" before the file is actually opened. It basically just hands it off to the application and then continues.

Another case is running Automator actions on Tiger. On Leopard, there is a mechanism to run them with the ability to wait for the them to complete but unfortunately, on Tiger, there's no such thing in place. Actually, on Tiger, there's no real official way to programmatically run Automator workflows but that's another story.

One workaround would be to mount the dmg using a script.

Is use the "open file" yes. So I should make an applescript that mounts instead?
The point is that I'm trying to have a clean desktop. So dropping dmg's on my sort folder and have it mounted and deleted would be a big help.

You could try an AppleScript or use a shell script which does 'hdiutil attach'. You'd have to play with it to see if it does wait for the mount to finish.