OpenBSD man pages and FAQ are really good too.
LLVM is not in the base install, but you can install clang from ports and build a program if you need to.
I agree with pledge() and arc4random(). They are both ridiculously easy to use. FreeBSD has Capsicum but it doesn't seem to be integrated.
Oh, and FreeBSD has DTrace. Judging from some recent commits it looks like OpenBSD is going to get some sort of tracing framework.