I was speaking to a guy recently and it came up that I was a software developer. He asked if I had majored in Computer Science. I told him no, my degree was in Philosophy. The guy was blown off his feet. What on earth could philosophy have to do with programming? It's never really seemed strange to me. So, here are some reasons why philosophers make good programmers.
One field of philosophy is Ontology, very loosely, the study of what there is. What things exist, what makes up reality. This same kind of thinking applies to object oriented design: what kinds of things should a program be made up of? It might sound esoteric, but being familiar with that kind of questioning makes object orientation feel pretty natural.
Another obvious one is formal logic. Boolean logic is foundational to computers, and studying other branches of logic prepares the mind for the kind of things a programmer does much better than mathematics. The kind of thinking you need to work out a proof in modal logic, or perform some feat with peano arithmetic feels very similar to debugging, or working through some sticky technical problem.
Philosophy of Science and Epistemology are both important to testing. I read Feyerabend's Against Method as one long argument for context-driven testing. Epistemology, the study of how we can have knowledge, is also relevant to the ambiguities I've faced as a software tester: how can I know a bug is gone? How can I know I've tested enough? Philosophy of Mind has only recently spawned Cognitive Science. Both are intimately linked with artificial intelligence.
Finally, and most generally, the whole orientation toward questioning what's best, what aims we should pursue and why, ties in closely to why I enjoy programming. There are endless ways I could write any particular program. In choosing a particular way, I'm discarding all the others. I had better have damned good reasons for doing so. (Many of the debates I see about the merits of various languages look a lot to me like philosophical arguments for the same reason.) Philosophy orients you toward doing things for reasons. And ultimately, that's the most important thing of all.