Primer (2004) cost only 7 grand to make, but is one of the best suspense/sci-fi movies I've ever seen. It's also a mind-bending experience like "Inception" and "Memento" and could require additional viewings or a rush to the Internet to figure out everything that's going on here. But it's a wonderful, trippy experience. (It's also available, either in parts or as a whole, on YouTube.)
Directed by Shane Carruth. With Shane Carruth, David Sullivan, Casey Gooden, Anand Upadhyaya. Four friends/fledgling entrepreneurs, knowing that there's something bigger and more innovative than the different error-checking devices they've built, wrestle over their new invention.