The latest internal Steam news update is now available, offering an update on the Lost Coast add-on. The update mentions that the new Half-Life 2 section, which will also come with High Dynamic Range lighting, is getting closer, though nothing specific is mentioned. Here's what comes after the Lost Coast release.

Once Lost Coast is released, we will include HDR in our future product releases. For instance, Day of Defeat: Source will feature HDR lighting for all of its levels the day it is released. One of the fundamental pieces of HDR rendering lies in "dynamic tonemapping." In the Source engine, by varying the exposure of a scene based on how much light is visible, we can accurately simulate a range of brightness that is beyond what a computer monitor is physically capable of displaying. A real-world example of this effect happens every time you walk from a very dark room to an outdoor area with very bright sunlight -- your eye takes a few moments to adjust to the variance in the amount of light hitting the retina. If you have a video card that supports HDR, you'll be able to see this in the engine when Lost Coast is released.

There's also a link to a video showing a side by side comparison between regular and HDR lighting.