Perfui!

I just spent an hour searching for the console command for source that shows your areaportals and visleafs in-game. I'm putting it here in case I ever forget and lest it's memory be stricken from the net. To see all your areaportals and visleafs in your source engine (hl2, tf2 etc) game, as well as other tools in a nice handy UI, open the console and type in "Perfui". You'll see a thing pop up. Have fun!