I compiled this list from a variety of sources. I tried to double-check them all, but I want to throw out a disclaimer that some may not be reliable. The information that’s available about domain name sales can be sketchy because many times the people who are doing the buying and selling don’t want to reveal information about their transactions because it can hurt them in future bargaining. So to the best of my knowledge, this is the most up-to-date list of domain names that have sold for millions of dollars.

poker.com – $20+ million – (I can’t find a reliable source for this – the domain was for sale by moniker.com at a silent auction in Amsterdam in May, but I can’t find a confirmation of who bought the domain or how much it went for. Rumors are more than $20 million)
sex.com  - $12 million
porn.com – $9.5 million
business.com – $7.5 million
diamond.com – $7.5 million
beer.com – $7 million
casino.com – $5.5 million
korea.com – $5 million
asseenontv.com – $5.1 million
seo.com – $5 million
shop.com – $3.5 million
altavista.com -  $3.3 million
loans.com – $3 million
vodka.com – $3 million
creditcheck.com – $3 million
wine.com – $2.9 million
creditcards.com – $2.75 million
autos.com – $2.2 million
express.com – $1.8 million
seniors.com – $1.5 million
tandberg.com – $1.5 million
cameras.com  - $1.5 million
vip.com – $1.4 million
scores.com – $1.18 million
chinese.com – $1.12 million
topix.com – $1 million
wallstreet.com – $1 million
rock.com – $1 million
poker.de – $957,937 – (This was the most expensive non-.com domain that I came across, so I thought I would include it)

Do you know of any others?

UPDATE:

computer.com – $2.2 million

guy.com – $1 million

invest.com – $1.015 million

Pizza.com – $2.6 million

~ Today’s view: http://www.flickr.com/photos/13799608@N08/1418435698/

I used the following sources in compiling this blog post:

Pacdesco.net Internet Marketing
Gagetopia.com
Royal Pingdom
Unhandled Perception
Wikipedia
Most-Expensive.net
Active-Domain.com 
DomainRich.com