Me? Jane Jacobs' Death and Life of Great American Cities. I read it when I was 21 (1998) and it changed how I walk down the street, every single day of my life since. Why this street is full of life, and that street is empty, for example. But not only that: she basically argues that central planning is disastrous for cities, and that cities should think on the street and human levels, from the ground up, and then iterate from there (rather than top-down). These ideas applied to other areas of life -- like software development, for example -- have been very powerful for me. I'd argue that Jacobs' thought is a precursor to the whole XP/agile software movement, for example. Both start with the same premise, the spec is dead (in software language). All this is probably obvious to y'all, but wasn't to me at 21 ;)
More recent sorta/kinda philosophy: "The Craftsman" by Richard Sennett; "From Novice to Expert: excellence and power in clinical nursing practice" by Patricia Benner; "The Craft of Thought: meditation, rhetoric, and the making of images, 400-1200" by Mary Carruthers.
I also like to think that "Asterix in Britain" by Goscinny and Uderzo had a formative influence on me...
I suspect that if you're not specifically looking for technical books you'd be better off looking at the common lists of 100 most popular books, or similar.
Me? I'd say "Dune", but that is only useful if you have an interest in sci-fi. If not then the Count of Monte Cristo is a glorious tale of revenge and plot. Beyond that recommendations become vague: Steven Brust, Zelazny, Tolkien, Pratchett & etc.
Aesop's Fables by Roger L'Estrange, 1715 3rd ed. in 2 volumes, ~900 pages total, otherwise it's an abridged edition.
Heraclitus complete fragments
When I see something in nature that speaks to a deeper level, that connects apparently unconnected things, that's as close as I get to a religious experience (i.e. not very close at all). For example, there's a cicada that has evolved a survival strategy based on prime numbers:
http://arachnoid.com/prime_numbers/index.html#Mathematical_L...
I always like finding examples that connect mathematics with nature, so this one was particularly satisfying.
My point? I can easily picture natural selection brutally filtering out everything that didn't make an ingenious (and chance) use of prime numbers to assure survival, but by the same token I can't picture nature caring at all what I think.