What was your first steam game?

Portal

Half Life & CounterStrike

My first game on Steam was Steam, according to https://store.steampowered.com/account

But if you really want to know, it was Portal :P

The Gundemonium Collection.

CS 1.6 :)

ATI Half-Life 2: Deathmatch / Half-Life 2: Lost Coast Promo on June 2, 2007.

I had an eMachines PC back then with no AGP or PCIe slots so I bought an ATI 9200 PCI card and it came with a claim code.

Retail copy of Counterstrike. I imagine it migrated me over to using Steam at some point.

L4D2

Half-Life 2 to me :)

Half-Life 1: Source

Dark messiah, one of the most hilarious games I've ever played

Magicka, on Nov 2011.

The first I bought was TF2, the one I got for free was Portal: The First Slice

Half-life orignal

First games I got on Steam were The Orange Box and Half-Life 1, followed by Garry's Mod the next day. May 30th and 31st, 2009.
And the irony of it all: I only got the Orange Box so I could actually play TF2 against someone, since there were so few players on the 360 version at the time. xD

Dota 2

TF2 + GMod.
Over 2600 combined hours and counting - by far my best purchase

The Orange Box: includes ‎Portal, ‎‎Half-Life 2, Half-Life 2 Episode One and ‎Half-Life 2 Episode Two

Team Fortress 2 in wednesday, September 17, 2008

...

12:46:02 GMT (and it was sunny)

Resident Evil 5, two months and a half banana ago.

Mine was Star Wars: KOTOR, gift from a friend that was sitting in my email for a few weeks before I even wanted to sign up for an account... then BAM here I am XD

Universe sandbox

Fallout: NV - fall of 2011.

Hldm2