I omitted the "one-day-only" because it would be too long. But what's on sale today won't be on sale tomorrow.
Today (in dollars):
GRID - 7.49
Champions Online - 19.99
Batman: Arkham Asylum - 24.99
Far Cry 2 + DLCs - 9.99
Fallen Earth - 24.99
Dragon Age: Origins - 37.49
Osmos - 2.00
THQ Complete Pack (including Red Faction: Guerrilla) - 49.99
Lucasarts Pack - 49.99
From here: http://store.steampowered.com/early-holiday
the words above were backed by NUCLEAR WEAPONS!