What are the cashback sites?
Some of the simplest cashback sites (CB) can be through your major credit cards, like "Shop Discover (DC)", Basically a click through purchase. For example DC currently has 5% CB for tigerdirect.com
Some of the 3rd party CB sites I've used include: fatwallet, mrrebates, and ebates (is it ok to list these here?)
The percentages range from 1% to 20%+, but generally 1-5%
If you make it a habit to put all your online purchases through a CB site it does ad up over time...