We pay for pretty much everything with a major credit card. At the end of the day, any credit card slips collected during the day are thrown into the back of one file folder. (Throwing them in the back keeps the folder sorted chronologically.) If the receipt is going to be tax deductible, we note that on the receipt before putting it in the file.
When credit card statements come in, we pull the file and match each item on the statement with the credit card slip. Any slip that is tax deductible gets put in a file labeled "Tax Deductible 2007" (or whatever the current year is). All of the other receipts get stapled to the statement, and we pay the bill.
There is a reference folder for each credit card we have. Once the bill is paid, the statement goes in the back of the file for that credit card.
We do not have to pull old receipts tat often, so we want a system that minimizes filing time, and what we have has worked beautifully since the Reagan administration. If we do have to pull a receipt, it's just a matter of thinking what card it would be on (which is not hard because we have one major credit card we use and then my wife has some individual store credit cards) and about when we bought it. We pull a couple of statements and scan the statement until we find the item. The receipt is going to be stapled to that statement. If it's not, it can only mean one thing--it's tax deductible and is going to be in the Tax Deductible 2007 and in order chronologically.