I've seen a lot of different "make money from your tweets" type of apps. Personally, I don't think I'd use it because I'd feel a little dishonest sharing things only to make money from my friends/followers, but Zocko is REALLY well designed.
They have tons of products that actually quite share-worthy (innovative new ideas, funny shirts, etc.) you can browse in a Pinterest-style interface. They tell you the price and how much you'll make off of each sale. You simply choose products you think your audience would like, and you share them.
Their email marketing is pretty well done too -- they email their members every week or so to share popular products.
Dododex