Steam sales mostly + an occasion trade for stuff I'm not able to purchase by myself.

Steam / Amazon purchases

Prostitution

Amazon/gamersgate/gmg bundles where you already own a couple of the things but it's still a good price for everything you don't have are good because they usually give you individual keys.

Crossbourne's secret key generator.

Steam/Amazon/GMG.

Sales, coupons, selling TF2 items I got for free on the market (100% discount :) ) and sometimes trading.

Amazon had some awesome offers during the October to January timeframe.

Traded my soul to the devil for Bad Rats

trading usually, and any games from bundles i got that i don't want

Scamming.
Duh! Easy as that

Sales mostly.

I fill out surveys. I might start to purchace bundles later on when I can buy stuff on the internet, but I think I should get a job before that happens.

For free obviously :P

Gamersgate pricing errors

I stole from the rich to give to the poor.

I usually buy games when they are on sale, from Steam, Greenmangaming, bundles etc. Steamgamesales.com is a good site for tracking which games are currently on sale, though the site has its flaws: it may occasionally show games that are not Steam redeemable and it doesn't include Amazon deals.

I just randomly find them in my inventory and if it's too common to profit off, I already have it or I dislike it, I just give it away.

I steal money from my mother.

Trading my items for some cheap games.

I rob Gamestop's physical locations and then give away the cd-keys.

Sales and bundles.

I buy them...

Sales, or CD keys of games I don't want.