Gliffy

I love Gliffy. I use it for logic flows and it works great.

I had to use this when my diagram exceeded the "complexity limit" of a LucidCharts trial. It's a little buggy (save early/often), but gets the job done and the price is right.

Works intuitively. It is useful for creating a wireframe before building the actual product and making a presentation document prior to a meeting. High-quality material helps you work efficiently.