We've always been huge fans of Valve's Meet the Team machinima (films made using video game software) films, and so we were very excited to see what would be birthed from the announcement that Valve would be releasing their machinima tools to the public in the form of Source Filmmaker.
So far the offerings are already pretty great. It's only been live for a short time though, so we expect things to continue to improve exponentially as more users get comfortable with the software. Here's the most highly-rated video currently available.
You can check out a bunch of other videos here in the official page where users post theirs films, and viewers vote and discuss which are the best.