I received a lot of recommendations (thanks everyone!) - here are the ones I have bought:
Building Domain Specific Languages in Boo
Writing Secure Code, Second Edition
Analysis Patterns Reusable Object Models (OBT)
How to Solve It: A New Aspect of Mathematical Method
Object Oriented Project Design
Extreme Programming Explained: Embrace Change
Getting Things Done: How to Achieve Stress-free Productivity
Here are the books that made it onto my "future" list which I didn't have enough cash for this time around.
I generally went for the cheaper books first, so that I could get as much input as possible. "The art of computer programming" looks good but I'd have hardly been able to get much else - especially as I considered Oren's book on DSLs a "must buy".
The "Patterns of software architecture" series look good, although I suspect the 3rd in the series is the equivalent of "Nightmare on Elm Street 2" because the table of contents don't look too good and all the second hand prices are much lower :-)
I wish I could just download this stuff straight into my head! Reading is so time consuming.