Choose from one of the following books for free when you sign up to a Safari Books Online trial:
Mastering CSS with Dreamweaver CS4;
The Hot Shoe Diaries: Big Light from Small Flashes;
Building Findable Websites: Web Standards, SEO, and Beyond;
The Adobe Photoshop Lightroom 2 Book: The Complete Guide for Photographers;
A Project Guide to UX Design;
The Photoshop Elements 7 Book for Digital Photographers;
Online Communities Handbook;
Facebook Me! A Guide to Having Fun with Your Friends and Promoting Your Projects on Facebook;
Mac OS X Leopard Killer Tips;
SocialCorp: Social Media Goes Corporate.
Simply sign up using the link, cancel your account immediately, then click the link in the 'Welcome' email to go and select your free book. I opted for the Mac OS X one, it's worth over $30!