Are there any websites that offer coupons for air travel?

The best place to look for this type of coupons is SearchAllDeals. Just start with a search term like "air travel coupons".

The Entertainment Book is a great resource for discounts on air travel. Not only that, they also have discounts on hotels, dining and entertainment once you get to your destination. You can purchase a book for practically any location online at www.entertaiment.com.

http://www.giantcodes.com/Travel-Codes/index.html

I know that Orbitz, Expedia and Travelocity offer coupons and deals that you can find out there on the net. I've included a few links to some pages with coupons from those companies.