Some tips for shipping (some of these may have already been mentioned):
-Bubble mailers work great for DVD size cases, I've never tried using one for a PS3 game, though.
-Check USPS.com and look to see what the hours are of the post offices near you, and whether or not they have an Automated Postage system. Try to find one that has a lobby open 24 hours with the automated system, that way you can ship stuff anytime day/night.
-Buy some labels, the post office only gives out free Priority mail and Express mail labels, and may reject packages if you try to use one on a 1st class package.
-If you ever ship via Priority mail, you can buy postage online from the USPS.com website. You will need a scale though to weigh your packages, and label sheets you run through a printer. The sheets can easily be found at any store that sells printer paper.
-Also, when shipping via Priority or Express, you can order free boxes from the USPS website.
-If you have time free during the day to actually visit a post office when staff is on duty, don't be afraid to ship APO/FPO (military bases). It's a really simple process (just one little form/label) and our troops greatly appreciate people that will trade/sell to them.
-Avoid international buyers/traders. Especially the Canadians.