I also have a few for purely nostalgic value, representative of key moments in my past. Notably: the OpenGL Red Book and C++ The Complete Reference.
- Microwave Transistor Amplifiers by Guillermo Gonzalez, which is a fantastic introduction and reference about high frequency circuit design
- The O'Reilly Linux Pocket guide, which has a cowboy on the cover and usually gets loaned to coworkers
Aside from that I've got a ton of sci-fi and high fantasy, but I'm slowly moving to a digital collection.
Then over time I just realised I could get pretty much anything non fiction related online, and stopped buying any more.
Might consider reading more novels in future though.