Perhaps not very hidden or necessarily innovative, but these are some of the Europe-developed games I have on my shelves
Darwinia - Introversion - UK
Zanzarah - Funatics - DE
Syberia - Microïds - FR
The Longest Journey - Funcom - NO
Max Payne - Remedy - FI
Cround Control - Massive - SE
Virus - Telstar (defunct) - UK

I've just realised that noone mentioned the most famous russian game: Tetris

Ha! Moonfear forgot Mafia, by Illusion software (CZ)!!
... Well, maybe he didn't, I didn't really enjoy that game myself
Anyway, UFOs are awesome! ... I think I've even posted about them somewhere around

never played mafia :) and I forgot Hidden and dangerous 2 too

England/Great Britain has always been part of Europa. Just because they are of the mainland doesn't mean anything else. Just like Japan is part of Asia, or Australia and New Zealand is Oceania etc.
And I'm surprised that no one has mentioned Arx Fatalis yet. It was made by the French company Arkane Studios.

Well if the french count tthen everything Delphine made was pretty damned awesome
If the poms count then Revolution has to rank as one of the best studios as well

Painkiller - People Can Fly - Poland
Penumbra - Frictional Games - Sweden

Finnish retail games :
Bugbear Entertainment
Rally Trophy (PC)(JoWood, 2001)
Tough Trucks (PC)(Activision, 2003)
Flatout 1 (PC, Xbox, PS2)(Empire Interactive, 2004)
Glimmerati (N-Gage)(Nokia, 2005)
Flatout 2 (PC, Xbox, PS2)(Empire Interactive, 2006)
Flatout: Ultimate Carnage (PC, XBOX 360)(Empire Interactive, 2007)
Sega Rally Revo (PSP)(Sega, 2007)
Flatout: Head On (PSP)(2007)
Encore Games
East India Company (PC)(Paradox Interactive, TBA (2009 est))
Frozenbyte
Shadowgrounds (PC) (2005)
Shadowgrounds Survivor (PC) (2007)
HouseMarque
Super Stardust (Amiga, CD32) (Team 17, 1995)
Super Stardust PC (PC) (Gametek, 1996)
Muukalaisten yö (eng. Alien Incident) (PC) (Gametek, 1996)
The Reap (PC) (Take 2, 1997)
Supreme Snowboarding (PC) (Infogrames, 1999)
Transworld Snowboarding (Xbox) (Atari, 1999)
Super Stardust HD (PS3) (Sony, 2007)
Golf: Tee It Up! (XBLA) (Activision, 2008)
Super Stardust Portable (PSP) (TBA)
Remedy Entertainment
Death Rally (PC)(Apogee, 1996)
Max Payne (PC, Mac, Xbox, PS2, GBA)(Rockstar Games, 2001)
Max Payne 2 (PC, Xbox, PS2)(Rockstar Games, 2003)
Alan Wake (PC, Xbox 360)(Microsoft, TBA)

Nival Interactive games.
Evil Islands-Really good RPG
Silent Storm-Jagged Alliance succesor
Heroes of Might and Magic 5-great sequel of legendary game
Nival is a Russian company.

You Are Empty - Digital Spray Studios (Russia)
Death To Spies (AKA SMERSH) - Haggard Games (Russia)

I'm surprised no one's mentioned Croteam yet, of Serious Sam fame
Serious Sam 2 was a failure though

Here are the contributions I can think of now:
Pathologic (IcePick Lodge) (Russia)
Tension / The Void (IcePick Lodge) (Russia)
Paradise Cracked (Mist Games) (Russia)
Cops: The Power of Law (Mist Games) (Russia)

The Arkania games and Drakensang you are thinking off?

yesssss I played shadows over riva alot

Chrome and Chrome Specforce - Techland sp. z.o.o. (Poland)