Valve is preparing to release a few updates to Half-Life 2 and Counter-Strike: Source over the next month or so via its content delivery system Steam, including new weapons for HL2 Deathmatch, a new single-player map showing off advanced lighting and an update for CS including a new map.
To begin with, Half-Life 2 Deathmatch will be updated with new weapons including the Slam, Stunstick and Crowbar. Valve had hoped to release the maps that won the HL2 DM map making competition in the same timeframe, but has decided instead to release these to tide people over while it continues to sort through them.
The new single-player map is actually a part of the Highway 17 chapter of Half-Life 2's single-player game. Called "The Lost Coast", it's been worked into a single level incorporating High Dynamic Range lighting "along with some new gameplay". Not that that tells us much; a bit of technobabble and an unquantifiable claim about in-game content. Still, a new single-player map!
Sadly though it won't be for everyone. According to Valve, "it will be made available free of charge to Half-Life 2 customers that meet a specific set of high end hardware requirements," which it plans to publish soon. You can see a concept sketch of how The Lost Coast will end up looking if you cast your eyes left and up. (Guessed, didja?)
Finally, Valve is planning to release a minor update to CS: Source that will address "a few minor issues", and will follow that up slightly later with the release of the "cs_compound" map.