There is a great little tool available from Effexis Software. Its called the Sequence Diagram Editor and allows users to rapidly build sequence diagram. Its sometimes referred to as UML lite.
The program works to let you quickly work with its intuitive interface. It comes with a 14 day free trial .
The price if you like it is $99.
I like tools like these, they are crisp in function and purpose. You get what you expect and the output is clear. I’m going to demo it for a few days on the free trial and provide some more information later on down the road with my thoughts.