When it comes to managing my receipts my organizational skills are questionable at best. I store some receipts in a designated manila envelope, some in a special box and all my online receipts are scattered across various e-mail addresses.
Lifehacker turned me on to a company called Shoeboxed, which has created a free online service that can automatically track and organize your online and offline purchases. When you make online purchases, you give the company your "@shoeboxed.com" e-mail address and stores will send receipts and e-mails directly to your Shoeboxed account. You can also one-click unsubscribe from store e-mail lists through Shoeboxed. They suggest that you can scan in or photograph your paper receipts and add them to your account as well, which sounds a little labor intensive, but is probably a great idea for those of us who travel for work and are constantly submitting invoices.