From their website:

Register any new domain (.COM, .US, .MOBI, .BIZ, .NET, .ORG, .CA, .CO.UK and .IN) for just $0.99* Use code: h4hp99

Register any new .com, .us, .mobi, .biz, .net, .org, .ca, .co.uk, and .in for just $0.99*. Plus ICANN fee of $0.18 per domain per year for .com, .mobi, .biz, .net, and .org. Discount applies to the first year only of one new registration. Cannot be used in conjunction with any other offer, sale, discount or promotion. Limited to one order per customer, expiring after 10,000 discount redemptions or at 11:59 PM PST on 7/31/2012 (whichever comes first). Customers may not use gift cards, PayPal? or AliPay to redeem this offer.