Free and open source, yEd is excellent for diagrams, flowcharts, BPMN, and so on. It is my go-to tool.
Commercial but free (requries registration), Bizagi Modeller is also very useful. It allows basic simulations such as bottleneck analysis by letting tokens run through your BPMN model, using %-chances you can configure at split gates. It's also slightly nicer looking by default.