Our inboxes are a treasure trove of digital receipts, forever lost beneath the weight of spam and cheesy e-mails from your mom. New York City-based OneReceipt hopes to take advantage of that valuable data with its new receipt tracking service, which will help you keep better track of your online and offline purchases.

The site has been in closed beta testing for a few months now and is today finally opening up to the public — just in time to help you chart your holiday shopping.

OneReceipt’s concept may sound familiar to you, as it directly competes with Lemon and Eric Schmidt-backed Slice. But co-founder Sam Fine tells VentureBeat that it differs significantly from both services. Lemon, for example, doesn’t automatically parse digital receipts in your e-mail account, you have to forward them to your Lemon account. And Slice doesn’t even tackle paper receipts yet (though it likely will eventually).

“We are going down the path of being the post-purchase hub for consumers,” Fine said in an e-mail. “After you make a purchase we want to be the location where people come to.”

Clearly, the time is ripe for receipt tracking services like OneReceipt to take off. Online shopping isn’t exactly going to disappear anytime soon, and, with the rise of smartphones and ubiquitous broadband, consumers are now more ready than ever to take advantage of services that make sense of typically useless data.

To use OneReceipt, you simply have to sign up and link an e-mail account to the service. The site will then begin scanning your e-mail account for receipts, and eventually it will present you with an elegant display of your purchases. For physical receipts, you need to take a photo with your phone and e-mail it to your OneReceipt e-mail address (dedicated mobile apps are on the way).

The site automatically categorizes your purchases (which you can change if need be), and you can also add tags for further details. OneReceipt also offers basic analytics, including your total monthly spending and purchases broken down by category. In my testing, I found that the site was a breeze to use and it accurately organized my spending without needing much help.

Fine and co-founder Michael Altman met at the University of Maryland, College Park, where they were accepted into the Hinman CEOs program. They pitched the initial idea for OneReceipt for their school’s business plan competition and ended up winning first place. After working on their careers for a few years, the pair decided to refocus on OneReceipt in 2010 with the goal of launching by the end of this year. They’re now working out of SkyLabs in New York City.

OneReceipt is currently free to use, but Fine says the company is exploring premium solutions for businesses, as well as making deals available based on your spending patterns.