Computational Geometry
I'm using the AAG's GIS Body of Knowledge
Numerical Recipes
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I really like Mapping Hacks
The book is divided up into 100 very creative 'hacks' that teach you about mapping, spatial data, opensource tools to work with data, and in the process inspire you to create or tackle the geospatial problems/hacks that you encounter in your work or personal life. One of my favorites is 'Will the Kids Barf'. It examines road sinuosity by comparing straight line distance with actual road distance to come up with an index to predict if the kids will get car sick.
This book It was published in 2005, so some of the references to APIs, etc. are a little dated, but the creativity, concepts, and inspiration are still very current.
PostGIS In Action
An excellent tutorial and resource on spatial databases in general and PostGIS in particular. The book is currently available through Manning's Early Access Program in .pdf format, the paper version will be out relatively soon.
Desktop GIS: Mapping the Planet with Open Source Tools
It's the first book I give out to folks when they're looking to learn a little about GIS and open source.
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A big list of transportation related GIS books. I'm biased towards transportation, but here a few books (mostly reference type) I cannot live without:
* Designing Geodatabases
* GIS for Transportation
* Field related: NCHRP Travel Demand Modeling (report 365)
* Field related: Transit Quality of Service Manual
* Field related: Forecasting Demographics
That covers it.