LivingSocial launched a 50% off deal at Whole Foods Markets today -- $10 for $20 in groceries -- the first time a national grocer has offered a daily deal with any company. Groupon did a deal with a New England supermarket chain in June and a grocery delivery service in April.

As of 3:30pm PT, nearly 960K Whole Foods deals had been purchased, meaning the cap of 1M purchases will likely be reached before the deal closes.

In January 2011, LivingSocial sold nearly 1.4M 50% off deals for Amazon gift cards (also $10 for $20 in purchases). Amazon invested $175M in the company in 2010.

Startup Aisle50, which came out of Y Combinator's summer 2011 class, gives one grocery deal every day reedemable with a grocery store loyalty card. Aisle50 makes the deal with the food manufacturer, however, not the grocery store. Aisle50 is only available in Lowes Foods stores in the eastern U.S.

Groupon is directly challenging Amazon in the U.K. with its 80%+ discounts on products sold online, according to a Bloomberg report.