You can always install Quicksilver. It's pretty handy. I've bound it to ctrl-alt-space, and F is enough to launch Firefox, M to launch Mail, I enough to launch

You can always install Quicksilver. It's pretty handy. I've bound it to ctrl-alt-space, and F is enough to launch Firefox, M to launch Mail, I enough to launch iTerm, etc., without creating shortcuts or editing settings. And if you want to launch some application with overlapping initials, type one or two more characters. And it's free.