In this holiday sale I bought:
Bioshock
C&C Red Alert 3: Uprising (6,79€)
C&C 3: Tiberium Wars + Kane's Wrath (6,79 €, too bad that you missed it)
Jedi Knight Collection (5 games) (old times, good times)
Killing Floor
Osmos (lovely)
STALKER: Clear Sky
Torchlight
Trials 2 (great fun!)
And L4D is for 17€, not above 20)
You want great games for less than 20€? (No particular order)
Braid (marvelous)
Torchlight
Bioshock
GTA: Vice City
GTA IV
Machinarium
Jedi Knight Collection
SW: Knights of the Old Republic (fantastic RPG)
Hitman 2
Hitman: BM
Company of Heroes: Gold (great strategic games set in WWII)
Killing Floor
STALKER: Shadow of Chernobyl (2€!!!)
World of Goo
Max Payne Bundle
Chronicles of Riddick: Assault on Dark Athena
Osmos (shiny)
Audiosurf (if you like music)
Indigo Prophecy
Beyond Good & Evil (a superb action game)
Painkiller: Black Edition (as above)
Sniper Elite
Evil Genius (you ever wanted to be a Bond villain?)
The Witcher (RPG of the year 2008)
Brothers in Arms: Hell's Highway
Plants vs Zombies (ever played a "defende the castle" game?)
That's the most I could find. And be quick about it, just 9 hours and 18 minutes left.
Oh and also:
http://steamcommunity.com/profiles/76561197998311690