What do you use to make programming flowcharts, diagrams, etc?

Microsoft Visio is pretty much designed for this task - whilst expensive, it's very good.

SmartDraw is great. Visio is good too, but not as feature-rich.

Google Docs has also recently added flowchart support too.

Graphviz is good for some type of diagrams.

Rational Software Modeler (used to be Rational Rose).

It also comes with a Microsoft .NET Extension that allows you to do .NET code generation from certain models.