Steam’s weekend deal for this week is a massive 66% Off their entire range of Half-Life games, including Half-Life 2 and all the episodes. You can buy the games individually, or buy all 8 titles for under $17 in the Half-Life pack.
If you’re an even bigger fan of Valve, then you can buy the complete Valve pack featuring every game the company has produced, and you’ll get 10% off the normal price during this weekend as well.