Found this on another site and hence sharing here, it may be helpful to someone looking for a cheap domain.

Use Coupon Code: Reddit399.

Details:
The coupon code can be applied when you're checking out in the cart on Domain.com

*LIMITED TIME OFFER. Reddit399 coupon expires September 30, 2011 at 11:59 pm Pacific. Reddit399 coupon is valid for one (1) .com, .net, .org, .info, .biz, and .us domain registration for one (1) year per account at the discounted price of $3.99 for the first registration year.

All renewals on products and services after the initial discounted period will be charged at the current standard list price for the selected period. Coupon is not valid with certain TLDs, existing products and services, renewals, transfers, custom website design, Sunrise registrations, Landrush registrations, other coupons, or special pricing.

I didn't try it myself though. Get it out till the promo is on. It expires tomorrow
nYXem Reviewed by nYXem on . $3.99 TLDs (.com, .net, .org, .info, .biz, and .us) Found this on another site and hence sharing here, it may be helpful to someone looking for a cheap domain. Use Coupon Code: Reddit399. Details: The coupon code can be applied when you're checking out in the cart on Domain.com *LIMITED TIME OFFER. Reddit399 coupon expires September 30, 2011 at 11:59 pm Pacific. Reddit399 coupon is valid for one (1) .com, .net, .org, .info, .biz, and .us domain registration for one (1) year per account at the discounted price of $3.99 for the first Rating: 5