I've been trying to think of a friend that I could gift HL2 to, but don't have many who play PC games. I was gonna give it to my roommate but he just bought the Orange Box so he's all set.
Thus, I have just HL2 to gift to anyone who would like it.
edit: It's gone. Gifted to Blur
Although it is three years old now and the HL2 singleplayer has not received the engine enhancements like the newer Source releases, it stills look surprisingly good (slightly low res textures and weak lighting and shadows is really the only things lacking) and most importantly it is a very fun campaign IMO. I liked HL2 singleplayer FAR more than than HL1. I never could finish HL1. IMO, the main reason that I liked HL1 and why it was (and is) hugely popular is because of the MP mods.