(I just wish I had such a discount code one week ago when I registered a lot of domains!)
gdr924y - 30% discount, expires September 27, 2009
gdp1148ab- 20% off over $70 expires Dec 1st, 2008. (GoDaddy)
gdp1208r- 20% off over $65 expires Dec 7th, 2008.
Other codes that usually work:
chill1, chill2, chill3