Apple’s OS X 10.7 adds new voices for text-to-speak, including a passable GladOS impersonation.
In the control panel, select the “Speech” icon.
Click the “Text to Speech” tab.
Select the pull down menu, and choose “Customize”.
Then select some new voices. I recommend adding Jill & Samantha. Also give Sangetta (Indian English), Fiona (Scottish), and Serena (United Kingdom) a try. Just keep in mind that each voice added has to be downloaded and is about a gig in size.
Ok, if you want your computer to sound like GladOS, get the Jill voice and then have her read the following:
There was even going to be a party for you. A big party that all your friends were invited to. I invited your best friend, the Companion Cube. Of course, he couldn’t come because you murdered him. All your other friends couldn’t come, either, because you don’t have any other friends because of how unlikable you are. It says so right here in your personnel file: “Unlikable. Liked by no one. A bitter, unlikable loner, whose passing shall not be mourned. Shall NOT be mourned.” That’s exactly what it says. Very formal. Very official. It also says you were adopted, so that’s funny, too.