The least used command in GM is the Applescript command, mostly because it requires learning another language. The only reason I decided to try it out was because, I thought I could find some stuff on the internet, and found out that you can also run Terminal commands through Applescript. and since I knew how to make it speak I wrote up this cmall little block
BEGIN APPLESCRIPT
do shell script "say kurt"
END APPLESCRIPT
very simple, and great reaction speed considering its running UNIX through Apple script through GameMaker.
For variations of the say command, that could make your game a bit more talkative. Check out my UNIX tut, or type 'man say' into the terminal.