Non-Steam Game you used to play.

Minecraft

It was Rune Halls of Valhalla for about 10 years of nonstop playing, but then it came to Steam, lol.

Warcraft III (including DotA), Populous: The Beginning, The Sims, SimCity 3000, Heroes of Might & Magic III, Guild Wars 2, Heroes of Newerth, just to name a few.

League of Legends and Smite :)

SimCity 3000

QWTF

Halo PC ♥

Simcity

Anyone remember Nox by Westwood Studios? I used to play that like a maniac. I bought it from GOG last year and played it through with all three classes. Still one of my favorite games ever. I've also poured countless hours to Minecraft. But then again, who hasn't?

Eden eternal

Final Fantasy VIII.

Battlefield 3, Rollercoaster Tycoon, trackmania nations forever, and some other.
I loveeee condemned criminal origins too, it wasn't available on steam untill a few months back :D

Tony Hawk series! :)

Rollercoaster Tycoon 1 + expansion and Warcraft 2 (later Warcraft 3 and wow when it was young. Ah good old days).

I also enjoyed The Sims until I broken one of the Expansions. As a kid, I thought you could install them in any sequence; which made "Living It Up" (my favorite expansion) crash my pc every time I used it D:

The Homeworld series. I'll jump through any hoops to install that from my original media if I really feel like playing it again. Which is likely.

Vindictus and Guild wars. And WoW but that's like... 2 years ago

swat 4

Way too many to name.

Soldat (on realistic servers mostly)

EVE online

Hmm. Thinking of non-Steam games that I played fanatically in the past, Return to Castle Wolfenstein: Enemy Territory, Infantry Online, and Diablo II are first ones to come to mind.

The original Unreal Tournament and it's 2004 sequel were two more of my favorite games, but I saw a SG for an Unreal Tournament Black(?), so I assume that franchise is already available on Steam.

Richard burns rally

Open Transport Tycoon Deluxe.

Minecraft.

I'd still play Atomic Bomberman if it wasn't IPX networking which it seems can't be done on W7 or later. :/

Hide and Seek when I was younger :P