I did mention this over in the Half-Life 2 topic 2 months ago, but I believe it deserves its own topic.
http://www.blackmesasource.com/
2008 trailer (they were too hopeful with the 2009 release date):
Basically it's a free, fan-made remake of Half-Life 1 that's been in production for the past 6 years, and I've been keeping an eye on it for just as long. According to
this article on Atomic, in August 2010 the game was "more or less complete - albeit with lots of tweaking to go - right up to the Xen levels". The website has updated recently (last week) with new imagery, and according to one of the developers on the forums, they aim to finally release this source mod 2 weeks after the soundtrack goes gold - And the soundtrack went gold last week. So I'm speculating that it'll probably be out within the next 2 or 3 months, although nothing has been officially confirmed yet.
Leaked screenshots of the first part of the game from August 2010 can be found here- And I have to say, it looks pretty damned fantastic considering it's a fan-made thing by people who are doing this as a hobby.
So yeah. Possibly coming soon. Possibly. :P
(although maybe not, knowing their history... lol)