During UX work there are many times when you need to build a flow chart, a sitemap or any other type of diagram. I've been using OmniGraffle on my Mac but at work I have to use a PC, so I gave Dia a try. Dia is great because it is versatile and also free. But I am wondering what is the best diagram tool out there. And by this I mean a versatile tool that could be used for creating any type of diagram. The tool could be web-based, free or paid.
Please share what tool you use and try to present it's strong and weak points.
Don't confuse diagrams with wireframes. Here are few examples of diagrams: