Until I saw this poster, I didn't think of subway maps as either beautiful or flowcharts. This one though, created by NYC graphic designer/illustrator Erin Jang, is both.
Erin's nephew's had a subway-themed birthday party and she made this one-glance map for him that includes all the places and subway stops that he'd rejoice over. Her nephew is three. I'm 37 and the subway in San Francisco is pretty useless, but I still want one.
So; you agree that this is beautiful certainly, but is it a flowchart? I think so. You have direction and process and you can map the results of your choices. Just because you're three years old and your choice is to see the Mets (too bad he can't take the subway to Fenway...) doesn't detract from it's essential flowchartiness (<- not actually a word).
Check out Erin's other work on her blog. She designs for Esquire magazine and specializes in custom wedding invitations for people like you. If you're in the glorious frenzy that is the pre-wedding black hole, she might be your savior.