Listmania!
On My Bookshelf
Professional PHP5 (Programmer to Programmer)Professional PHP5 (Programmer to Programmer) by Edward Lecky-Thompson
Buy new: £22.94 / Used from: £11.67
An excellent book for advancing your skills beyond simple websites
Pro PHP SecurityPro PHP Security by Chris; Southwell, Michael Snyder
Buy new: £25.76 / Used from: £17.83
Some very good security tips and tricks.
Mind Hacks: Tips & Tricks for Using Your Brain: Tips and Tricks for Using Your BrainMind Hacks: Tips & Tricks for Using Your Brain: Tips and Tricks for Using Your Brain by Tom Stafford
Buy new: £10.27 / Used from: £9.42
Brought this at a conference but have yet to read it!
Subversion Version Control: Using the Subversion Version Control System in Development Projects (Bruce Perens' Open Source)Subversion Version Control: Using the Subversion Version Control System in Development Projects (Bruce Perens' Open Source) by William Nagel
Buy new: £24.64 / Used from: £17.00
Offers some good tips and case studies that you cannot find on svnbook.red-bean.com
CSS: The Definitive GuideCSS: The Definitive Guide by Eric Meyer
Buy new: £18.82 / Used from: £18.00
Another book I brought at a conference but have yet to read
Designing Web Navigation: Optimizing the User ExperienceDesigning Web Navigation: Optimizing the User Experience by James Kalbach
Buy new: £20.03 / Used from: £20.00
A nice colourful book on web navigation. An interesting read if you are more of a designer
The Little SchemerThe Little Schemer by DP Friedman
Buy new: £16.00 / Used from: £15.52
A very intersting book on functional programming (was originally 'The Little Lisper'). It will make you brain hurt!
Head First Design PatternsHead First Design Patterns by Eric Freeman
Buy new: £19.82 / Used from: £15.99
I get the impression that this is one of many great books from the Head First series, may not be techie enough for some though.
The  C Programming Language (2nd Edition)The C Programming Language (2nd Edition) by Brian W. Kernighan
Buy new: £19.16 / Used from: £12.00
While deceptively thin, this book covers the whole C language and is written by its makers. When I get the time I will read this book and then I will finally know C.
Object-oriented Programming in C++Object-oriented Programming in C++ by Robert Lafore
Buy new: £22.19 / Used from: £20.00
I will read this one once I have read the (much thinner!) 'The C Programming Language'