A while back, valve stated that shortly after the release of the game, there would be a surprise for thoes who are dissapointed that Counter-Strike was the only multiplayer included in HL2....
nothing more was said on the subject, and people started to dismiss it saying it was nothing or some said it was Half-Life source was the surprise...
Well now according to planet half-life, along with the new patch to fix the stuttering problem... they also said...
"Next week we will be releasing the Source SDK, along with a surprise for the community."

im REALLY hoping for either an official HL2 multiplayer, or Team Fortress.
but i have a feeling i'll be dissapointed by the 'surprise' lol.
*waits for next week to come...*