eBay
Before you pay full price for something, check eBay. Many times you can find the item you are looking for, used or even new, at a good price. You can search Completed Items to find what items have been selling for, then place your maximum bid for the item.

Restaurant.com
Restaurant.com offers signficantly discounted gift certificates to selected restaurants throughout the country. $25 certificates are available for $10.00 and $10 certificates are available for $3.00. Search by zip code to find the participating restaurants in your area (or perhaps in an area where you are planning to vacation).

Amazon.com
Amazon has grown from being primarily an online book retailer to being an online retailer of almost anything. In addition to new items, many individual sellers list their new and used items for sale on Amazon. There is usually some good competition on prices, but remember to add on the shipping charge.

Craig's List
Craigs List has become the de facto classifieds of the internet. You can select a country, state, and major city and then search for items for sale in that local area. In addition to the For Sale category, Craigs List also includes listings of gigs, jobs, housing (for sale or rent), services, and a community section.

Remember, when buying or selling on CraigsList, to always meet the person (you are buying or selling with) in person, as that will prevent 99% of potential scams.