"The wmctrl program is just what you're looking for (sudo apt-get install wmctrl). You can use the wmctrl -a ""AppTitle"" command to bring the app to the front. wmctrl -l will list all available windows, so it should be easy to write a shell script that checks if your program is running and either launches it or brings it to the front. Then you can just bind that to a keyboard shortcut.
First save the following script somewhere, I'll use /home/jtb/code/bringToFront. It takes two arguments, the first is what you would type at the terminal to launch the program, the second is a substring of the program window's title. If there is no constant unique string in the title then you'll need to do a bit more work to find the program's window.
#!/bin/bash
if [ `wmctrl -l | grep -c ""$2""` != 0 ]
then
wmctrl -a ""$2""
else
$1 &
fi
With the script in your current directory, run chmod +x bringToFront to make the script executable. Then make sure it works; to launch/focus firefox you could run ./bringToFront firefox ""Mozilla Firefox"".
Now we need to bind a shortcut key. Run gconf-editor and navigate the folder structure to the left to /apps/metacity/keybinding_commands.
Double click on the first command with a blank value, probably command_1. Type the full path to the script and provide the two parameters, e.g. /home/jtb/code/bringToFront firefox Firefox.
From the panel on the left, select global_keybindings, the next folder up. Find the run entry matching the command you just defined, probably run_command_1. Double click it and type the keyboard shortcut you want to use. Put the modifiers in angle brackets, e.g. <Ctrl><Alt>F.
Now Control + Alt + F will bring your firefox window to the front, or launch it if it's not already running."
