If you ever buy from Groupon, did you know that you can always get an additional 6% off (in the form of a cash-back rebate)? You can do this by visiting Groupon via Ebates.com or FatWallet.com.
For that matter, you can earn cash-back (or other rewards) rebates when buying just about ANYTHING online. For more details, I'll point you to a previous post from my website HERE.
Groupon is currently also running a coupon deal today and tomorrow only (through 9/9) for 15% off any one Groupon "local" deal (things such as restaurants). Use the coupon code "LOCAL15". You should be able to use the coupon code and earn the cash-back rebate (but note that sometimes the cash-back rebates can be invalidated by the use of a coupon code - unless the coupon code is listed on the cash-back rebate website).
A particularly nice deal (if you live in the Portland area) right now would be to use the 15% + 6% off to buy a voucher for 2 movies + a free concession voucher at any of the 3 Cinetopia movie theaters for $19.95 (price before the discounts). Just go to Groupon and search for "Cinetopia". Considering some 3D movies and/or shows in some of their specialty "movie parlor" or "living room" theaters can be as much as $20 per ticket (!!!), paying less than $16 for a pair of tickets and some free popcorn or coke is a pretty good deal.