If you didn't grab Warhammer 40,000: Space Marine for $25 via GamersGate last week, Steam has it for only $17 as part of its "Warhammer Weekend" promotion. You'll also find 66% off seemingly every other game in the franchise as well as their DLC packs and last May's Section 8: Prejudice. Meanwhile, GameStop still offers 50-60% Dungeon Siege III and Tropico 4, and Good Old Games cuts half off Activision Quest titles (King's Quest, Police Quest and Space Quest).

Steam
75 Warhammer 40,000: Space Marine $16.99 (66% off)
Warhammer 40,000 Dawn of War II - Complete Pack $20.39 (66% off)
69 Dawn of War - Platinum Edition $10.19 (66% off)
74 Section 8: Prejudice $5.09 (66% off)
62  Earth Defense Force: Insect Armageddon $14.99 (25% off)
More... (tons of DLC)

GameStop
78 Victoria II $19.99 (33% off)
67 Dungeon Siege III $19.99 (60% off)
88 GTA: Episodes from Libery City $19.99 (33% off)
81 Tropico 3 $9.99 (33% off)
78 Tropico 4 $19.99 (50% off)
More...

GamersGate
47 Afterfall: Insanity $19.99 (43% off)
Metacell $4.99 (50% off)
Shattered Origins: Guardians of Unity $14.96 (25% off)
Jagged Alliance 2 $3.40 (66% off)
More...

Green Man Gaming
75 Two Worlds II $31.99 (20% off)
52 The First Templar $21.79 (27% off)
85 Super Meat Boy $9.98 (33% off)
UFO: Afterlight $11.96 (20% off)
More...

Good Old Games
50% off Activision Quests