I am a huge fan of the Lucky Rewards program. You have to be a subscriber to Lucky Magazine, which is a "magalog" full of fun and stylish things to buy. A subscription costs $12. My subscription has already paid for itself thrice over. How? Because I use the links on the Lucky Rewards website to buy things I was going to buy anyway.
Take, for instance, the two pairs of spring shoes I bought on Zappos.com. They were on sale, so yay. Additionally, Zappos rocks because they have free overnight shipping and free returns: double yay. I get 1% back on my Amazon Visa regardless (not the best cash back program, but okay), but through Lucky Rewards I get an additional 14% back.
Not all the Lucky Rewards discounts are that steep, but they do offer discounts at a lot of different places, and sometimes they can really knock down your total expense. Skinstore.com, where nearly all of the products for this comprehensive skin care regime can be found, gives a 13% discount. You can also order movie passes for $8 each and get 25% of that back from Lucky Rewards, although I haven't tried that yet. If you have certain things that you buy frequently from vendors on this list, subscribing might be worthwhile.
Another great site that I found recently is The Bargainist. Today I got a $75 book I've been wanting for ages for $56, thanks to a coupon code from The Bargainist and Lucky Rewards.