I always check Travelzoo - especially their top 20. I have linked to four or five GREAT travel deals form their list - including a trip to China with air and hotels for $650, and some discounted deals with Gate1 (another fine company for me).
Since Southwest opened a hub here in my Baltimore, I have flown with them at least 30 times without a problem within their control. I so appreciate the transparency of their pricing and the ability to book legs separately. Great value, great sales, and for the most part - great staff and in-air service.
My only problem was missing the expirations. I was so pleased when the paid value became good forever. And just recently - they emailed me with an offer to let me trade in an expired groupon for value on a new purchase! Fantastic idea!
I've used Living Social for years and found some great local companies - who have earned ongoing business from me. Yes, there were some losers, but LS's revised refund/cancellation policy has made it worthwhile to take the occasional risk. You have to stay on top of the timing and deadlines. So fun to find things I wouldn't otherwise have tried.