CaptLinger
CAGiversary!
I know there have been several posts for Groupon and the codes are hit-or-miss. This certainly missed me! This one is only good for 5-31. It's $10 off at checkout: QUICK10. Here's a FAQ on their promo codes:
https://www.groupon.com/faq#faqs:category-76
https://www.groupon.com/faq#faqs:category-76