Is there any Standard ANSI/ASME flowcharts? My interest is in processes with human – machine interaction. e.g. car driving, buying in vending machine, among others.
UML: Should be a good choice, since it produces nice pictures ;) - I'd suggest looking at Activity Diagrams (as mentioned before) and at Sequence Charts. The latter one also allows for presenting more details on the interaction
On top of UML, you could use SysML (but not sure if this is too big)
You can also have a look at the FMC language: http://www.fmc-modeling.org/
The notation depends on the audience that you need to address. Can you give some details on that? If you have to talk to techies then maybe Matlab/Simulink is also an idea as those generate more technical models (also visuals...).