6) Loyalty programs
Some companies have begun offering loyalty discounts if you stay with them. For example, Western Digital gives their customers a discount on newer drives if you have one of their older models. The drive can be in warranty or out of warranty, it does not matter. All you will need to provide them is a valid serial number off your old internal drive and they'll provide you with a discount on a new one. You do not even need to send in your old drive!
Wester Digital Loyalty
As much as I hate to list this site, it has to land somewhere in the middle of the list. One reason why I do not like eBay all that much is there is absolutely no way to guarantee you are getting what the auction is stating. Most sellers are not big businesses and because of that, warranties and returns are next to none. However, if you have a keen eye, you can spot some diamonds in the rough. For example, a user on Anandtech's forums found a 50" Sony Plasma TV that would turn on, but turn off immediately afterwards. The seller in the auction stated that the Y-drive board may need replacing in the unit, which would cost around $920. The buyer found an estimate locally for about half that price. So after winning the auction at a little over $400, he went and purchased a service manual. After checking out the unit and referencing the troubleshooting section of the manual, the plasma did not need the Y-drive replaced. It just needed the temp sensor to be reattached. Netting a 50" plasma for a bit over $400 and the price of a $20 manual equates to a smoking hot deal. Your mileage will definitely vary on eBay as most deals will not be like this. Just be careful of what you bid on and make sure to research the seller's feedback.
You can think of Craigslist as eBay without the hassle of auctions. Users can post items or services up for sale and other users can contact the seller directly for purchases. Since Craigslist is positioned to categorize listings in local areas, the shipping process can be eliminated. After contacting the seller, the buyer can ask to meet someone to exchange goods. Often times, you'll find a lot of people who want to off-load items quickly due to moving or simply wanting to clean out their house. I've seen a few people score some cheap Macbooks from other users who just wanted to upgrade.