1.Structured Programming (be sure to look at the argument that E. Dijkstra made in his famous paper "GOTO Considered Harmful.").
2.Nassi-Shneiderman sructure charts (yes, that's Ben Shneiderman, before he became famous for his work in HCI).
3.Formal proofs of correctness.
4.Structured Analysis and Design (with dataflow diagrams).