While the Black Mesa team is busy not overhauling Half-Life and Valve is busy not making Half-Life 2: Episode Three, a modder by the name of Filip Victor has updated the graphical components of Half-Life 2 and Half-Life 2: Episode 2, making it even shinier than before.
Half-Life 2: Update packs the Orange Box Engine, High Dynamic Range lighting (if you don't know what that is: you like it, a lot), new models and textures, and 32 Steam Achievements. Naturally, you'll need Half-Life 2 & Half-Life 2 : Episode Two to make use of the goods, but if you're reading this, you probably already have them.
See the change in action below (be sure to watch in HD), and grab Update via the source at bottom, or with this torrent.
Word from Valve is they'll be releasing something similar in the future, bringing the game on par with the updated 360 version. Another project is commentary for the original Half-Life.