Late to the party but came across this while searching for something else and thought I'd throw in my two cents. Lucidchart is a sweet web app for this. Use on my Mac and wife's PC.

I have used an older version of Omnigraffle, which has some cute stuff, but I never paid for the full version and can't vouch for it. (For reference, I used it to make a discussion-tree for volunteers calling former donors about a non-profit conservation organization -- i.e., if the person picks up the phone and is interested, what do you say next?)

there is a product called omnigraffle (omnigroup.com), quite visio-esque, though it costs $150. macworld reviewed it in tandem with something cheaper, but i can't find it at the moment...

Can anyone recommend a good flowchart-making program for OSX? I'm ideally looking for something cheap/free, lightweight, and very task-specific, but willing to sacrifice all of these criteria if necessary.  

Thanks.