"The non-designer's design book" is really great, I learned a lot from it. It helps to know these things, even though I am a software developer and normally do little to no design work for my clients.
Currently I read "Visual Language for Designers" (-) which is also very interesting. It describes how our brain processes visual information and how you can use this to create better (easier to understand) designs.
If you are interested in the theory design and if you can find them (no, they're not the A-Team, just maybe out of print), have a look at "Design and Form" and "The Elements of Colour" both by Johannes Itten and "Principles of Form and Design" by Wucious Wong.
Somebody also suggested "The Design of Design: Essays from a Computer Scientist", by Frederick P. Brooks (Mythical Man Month) ... http://amzn.to/ueRrkv
I really loved - not something that happens often to me - "Designing visual interfaces" by Mullet and Sano. The examples are dated now, but the techniques and the suggestions are pure gold.
Currently I read "Visual Language for Designers" (-) which is also very interesting. It describes how our brain processes visual information and how you can use this to create better (easier to understand) designs.
(-) http://www.amazon.com/Visual-Language-Designers-Principles-U...