GoDaddy has a one week deal for a co domain at a price of just $9.49 until 7 PM Central time on June 6th. You can get as many as you like. That is 68% off the regular $30 price.
Visit godaddy here and use the .co domain coupon code: dotco949 for $9.49 .co domains.
The last .co coupon was available for a month and was for $10.49, this is obviously a better coupon but only available for a week.