For my purposes (embedded), UML statecharts are as good as any other way to do statecharts, and sequence diagrams are occasionally useful. The 10,000 foot view you started off with of big program blocks, also, especially to just draw out the processes in a system.

The complementary question, though, is how do you visualize data when coding? Some debuggers have features for visualizing data structures, time-series data, etc but there is plenty of room for improvement.