Ask HN: What library should be my geospatial "swiss army knife"?

Googling around I was having a hard time determining which geospatial library to learn as my "swiss army knife" for data exploration and perhaps some production code. I'm not particular about the language, although our existing infrastructure is mostly C, Java, and Ruby.

I've played with SimpleGeo in Ruby and GDAL in C. I'm looking towards using Java libs with JRuby for other reasons but the question at hand is a broader one: what languages/libraries do you use for spatial data analysis?