There are 3 levels of compatibility that the WINE project recognizes regarding native windows applications running on WINE. These follow a sort of Olympics theme:

Platinum: Applications which install and run flawlessly on an out-of-the-box Wine installation

Gold: Applications that work flawlessly with some special configuration

Silver: Applications with minor issues that do not affect typical usage

As of today; 12-29-09, the 10 top games according to user voting in WineHQ.org are:

Platinum Rated Game List
  1) Star Craft: Brood Wars
  2) Guild Wars
  3) Photoshop CS2
  4) Counter Strike (Retail and Steam versions)
  5) Supreme Commander
  6) Half-Life 2
  7) Watchtower Library
  8) Silkroad Online
  9) Spore
10) Day of Defeat (Steam version)

Gold Rated Game List
  1) Eve Online: Dominion
  2) Steam Online Gaming Client (all versions)
  3) The Sims 3
  4) Bio Shock
  5) Runes of Magic
  6) Homeworld 2
  7) System Shock 2
  8) Planetscape: Torment
  9) Soldat
10) S.T.A.L.K.E.R. Shadow of Chernobyl

Silver Rated Game List
  1) Final Fantasy XI Online
  2) Warhammer Online Live
  3) World of Warcraft
  4) Fallout 3
  5) Team Fortress 2 (Steam version)
  6) Aion: The Tower of Eternity (versions after 1.5.0.6)
  7) Left 4 Dead (Full version from Steam)
  8) Command & Conquer 3: Tiberium Wars
  9) Warcraft 3: The Frozen Throne
10) Call of Duty 4: Modern Warfare

Please keep in mind that regardless of the overall rating of these titles, if it is your intention to play one of these titles on GNU/Linux utilizing WINE then you should visit the WineHQ.org and look up the title. There may be comments from other players that have some tips on configuring the game client to play best under WINE.