This tutorial will help you to hopefully get software and possibly products for almost free.
It won't work on products because it sends the seller an email along the lines of "you have received $0.01 from (your paypal name) for (the product)" However this works great on automated software scripts where it detects that you gave a payment and emails you a link to download the software.

You will need the Firefox extension Tamper Data for this to work.
Download it here: link to download tamper data

Step 2: Finding your target

Now for the most important part, modifying the post variables.
Find the parameter called amount and change the value to 0.01 because that is the lowest amount PayPal will process. Next mess with the parameter called no_shipping, if it is even there, until your shipping comes out free. When you are done click the OK button at the bottom of the window.

Step 6: Finished