[bharyms]

Lekh Diagram (http://www.avabodh.com/lekh) Quick way to draw flowchart, block diagram etc. Only available for iOS though.

[alok-g]

I had tried Lekh Diagram and Grafio both and found the latter to be better. You may want to try it out.

http://www.tentouchapps.com/grafio

[rajeevk]

Lekh has better shape recognition and shape customizibility.

- you can resize vertically and horizontally independently which grafio can not

- you can move vertices of any polygon.

- You can draw bezier curve and modify it to any shape by changing the control points.

-Lekh recognizes different kinds of connections from your drawing.