Groups like McCall's Patterns have a pattern of the week that you can buy for $2.99 that week (instead of the regular $15-$20). Origins lets you get a free sample for liking their page. They tend to change their samples fairly often so you can get new samples all the time.
|Just friend the Origins page on FB to get this freebie|
One of my favorites is the Bath and Body Works page. They constantly have coupons for free items. I've gotten a small candle and a 2oz bottle of their new lotion. All for clicking that little like button.
One of the great things about Facebook is that if you get tired of reading their pages you can hide it from your feed and choose when you want to read their fan pages. Just make sure you check back for all those great offers.