The Purchase Brothers (their website is currently squished by traffic), independent filmmakers and commercial directors, have released the first part of their Half-Life-inspired short film series. And it's pretty good. It's a mixture of live action and game footage, and makes smart use of in-game sound effects, and some really fantastic location hunting. Originally developed to test post-production techniques for their work, as well as to create a 'spec' commercial to demonstrate their talents, it eventually became a series of shorts telling a story within the Half-Life universe. And it's below.
The Purchase Bros describe the production as "guerilla style with no money, no time, no crew, no script, the first two episodes were made from beginning to end on a budget of $500." The project has been made with the full support of Valve, who gave the project a plug on the instantly-disappearing Steam Update News. Make sure to select to watch it in HD (the option appears bottom right after you've clicked play).