Portal is free until May 24th. Also, it's on Mac now.
 

Exactly what it says on the tin. All you'll need is Steam.

http://store.steampowered.com/freeportal/

Now I wish I didn't have it so I could get it again, and again. I love Valve.

Sadly, Steam isn't working for me. Curses.

Of course it isn't. C'mon one of the biggest games is being downloaded for free.

I beat it, but traded it in when I got TF2 for the PC. please, PLEASE let this include the extra levels

There are extra levels? O_o

Oh thank you Token a thousand times for announcing this. I tried to buy Portal last year, but my computer (purchased in 2004) could not run it. I've since bought a new computer, but haven't thought of trying to get Portal again. Now I can for free! HAHA!

they released it as a DLC for 360 version awhile back, not sure what they did for it on the PC end

Not being able to afford everything at once has it's advantages... for once!

The extra levels are FREE on PC, you only had to pay for them on the XBOX 360, as they needed editing to work on that. They were borrowed and modified from Portal the Flash Map Pack.

Sadly, I already own the game, the mods, and have beaten it to every possible extent possible. Lucky blokes, something made free that I already paid for, when I'm the king of the free lunch!