Black, Battlefront II added to the list, while other big titles receive improved compatibility.
While the Xbox 360's backwards compatibility with Xbox games has come under a lot of criticism, mainly due to the small number of games that work at a satisfactory level, a few new games were added to the list of supported titles today. EA's Black and LucasArts' Star Wars: Battlefront II are now both playable on the Xbox 360, assuming you have a hard drive and can connect to Xbox Live to download the update.
Other games that were already on the list are also said to have benefited from improved performance, with big titles such as Grand Theft Auto: San Andreas, Half-Life 2, Fable, Fable: The Lost Chapters, Forza Motorsport, Ninja Gaiden, Ninja Gaiden Black and Tom Clancy's Splinter Cell Chaos Theory being the most important of the bunch.
The UK portion of Xbox.com isn't showing the updated backwards compatibility list yet, but if and when it's updated it can be found here.