As noted by Kotaku, Valve Software is set to launch the Mac OS X version of Half-Life 2 today, with follow-up sequels Half-Life 2: Episode One and Half-Life 2: Episode Two also seeing their public release for the platform.
Valve announced in early March that it would be bringing its Steam game distribution platform and library of games to Mac OS X, with the public release going live earlier this month. Among the 60 launch titles for Mac OS X was Valve's Portal, which was available for free until earlier this week.
Valve will continue to roll out new titles for the Mac on a regular basis, with the Half-Life 2 package representing the next step in that process. To celebrate the launch of Half-Life 2, Valve has remade a portion of Apple's iconic 1984 Super Bowl commercial in a Half-Life 2-inspired theme, with series protagonist Alyx Vance serving as the main character in the promo. Several frames of the remake were used in one of six leaked teaser images sent to MacRumors and other sites ahead of Valve's official Mac announcement.
Update: The three Half-Life 2 titles have now been updated, with support for Mac OS X obviously being the most significant item of interest for Mac users. The titles are temporarily on sale at 30% off, with Half-Life 2 priced at $6.99 (down from $9.99) and Episode One and Two available for $5.59 each (down from $7.99).