Dotster currently has a sale on .net domain names which are going for $8.99 per domain name per year. Their .com domains go for $15.95 per domain name per year and they charge $6.99 per domain name per year if you want to protect your registration information from the WHOIS database.
At the time of research, [...]

GoDaddy currently has a special rate of $1.99 for any domain (.com, .us, .mobi, .biz, .net, or .me) but you need to read the fine print carefully:

The special rate of $1.99 per domain name per year only lasts for the first year. After that, the price goes back to $10.69 per domain per year [...]

We use Bluehost to host our websites. We used to love them, but they’ve changed their domain name privacy registration policy and so now we’re looking elsewhere to buy our domain names.
Bluehost used to charge $10 per domain name per year, which is a tad on the pricey side, but it came with free Domain [...]

Update (Dec 2009): DynoNames.com still offers their sale on .info domain names: $1.99 per domain name for the first year before eventually returning to the regular price of  $7.39 per domain name per year. If you try to buy a domain name with DynoNames, you’ll find it’s really a Wild West Reseller. Check out our domain [...]

Update (Dec 2009): DomainsAreFree.com still offers a sale price on .com, .org and .net domains:  $3.99 per domain name for the first year before returning to the regular price of $14.95 per domain name per year. Domain privacy is now listed as $8.99 per domain name per year. There are domain registrars that offer cheaper [...]