5. 'Primer' (2004)
A rigorous, graduate-level time-travel movie, full of confusing plot twists, technical jargon, and duplicate versions of characters trying to outfox each other. But it's also a thrilling mind-bender, and as soon as you're done watching it, you want to see the whole thing again to see if it actually makes sense. (It does). Made for an astonishingly low $7,000, director Shane Carruth's debut is also one of the best movies ever about a tech start-up: When some engineer friends make a working time machine, they skip right over the ethical consequences in favor of the financial rewards.