Get $10 off any $50+ purchase at Lowes home improvement stores in-store or online. Expires 11/15/2013. Sign up for AmEx Sync first if you haven’t already. Then tweet anything with #AmexLowes. You should get a confirmation reply quickly. Details here.
You may also be able to access these discounts via Facebook, the AmEx smartphone app, or by simply logging into your account online. Twitter has worked reliably for me. I post a lot of smaller and time-sensitive deals like this on my Twitter feed @mymoneyblog, which are echoed on my Facebook page.