Well, Davey Shafik started it with this post on his blog, and Firman Wandayandi (of DotGeek) continues it - a listing of "references on their desktop" - books/magazines/etc that are around them at all times for their reference.

From Davey:

Mine are:

• Sams Teach Yourself MySQL in 10 Minutes
• JavaScript: The Definitive Guide
• Essential PHP Security
• XSLT
• PHP|Architect's Guide to PHP Design Patterns
• The latest issue of php|architect

And Firman's:

• Wrox Professional CSS Cascading Style Sheets for Web Design
• Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley Professional Computing Series)
• Manning Ajax in Action
• PHP|Architect issues
• PHP Manual
• PEAR Manual

What kind of reference materials do you use? What books are on your desk that never seem to collect dust because is seems like they're always in use? Do you have one of the giant PHP posters on your wall that SitePoint was offering? Post your comments below!