Manning, publisher of books such as The Well Grounded Rubyist and Ruby in Practice (and many others) are offering a 35% discount to everyone attending the conference. You could even pre-order Rails 3 in Action (due in February 2010, but available via early access)
You can also browse the O'Reilly book catalogue - Josette from O'Reilly will be at the conference, selling a host of books at special rates!
I'm very happy that rails hosting providers, Brightbox are supporting us too! Brightbox provide UK hosting services tailored specifically for Rails. Visit their web site for more details.