Sounds like a good movie to me...

Primer, a new indie sci-fi movie.

Here's an excerpt of the review from C.H.U.D.:

Here’s the basics of the plot: Abe and Aaron are friends, engineers, who spend their time in the garage trying to hammer out new patents. They want to make something that will make them rich and while trying to create some sort of a device that can make objects lighter (the concept is that it would revolutionize shipping and travel), they accidentally invent a time machine.

The mechanics are complicated, but the machine allows them to travel back in time a few hours. They immediately begin using it to play the stock market. In fact, it’s the very first thing they do with it. Soon, though, things begin to get darker as the true level of power inherent in even limited time travel becomes obvious. And that’s before they realize they can take the machines back in time with them.