Apple has released Snow Leopard Graphics Update 1.0 to solve specific issues regarding frame rates in Portal and Team Fortress 2 on certain Macs, as well as issues that could cause StarCraft II or Aperture 3 to quit unexpectedly or become unresponsive.
The Graphics Update 1.0 release also corrects an image-corruption issue that appears when disconnecting and reconnecting external displays.
The update is 69.2MB and is available via Software Update for Macs running Mac OS X 10.6.4.
According to the Apple knowledge base article about the update, the products affected are:
MacBook (13-inch, Early 2009), MacBook Pro (17-inch, Mid 2010), MacBook Pro (13-inch, Mid 2010), MacBook Pro (15-inch, Mid 2010), iMac (21.5-inch, Late 2009), Mac Pro (Early 2009), Mac mini (Early 2009), Mac OS X 10.6.4, Mac mini (Mid 2010), iMac (21.5-inch, Mid 2010), iMac (27-inch, Mid 2010), MacBook (13-inch, Mid 2010), Portal, StarCraft II, Team Fortress 2