I know you asked about pretty picture graphs, but I will second Stuart's recommendation of nfdump. Graphs may be pretty but if you want to dig into the data nfdump is very useful.
diana On Mon, 1 Jun 2009, Stuart Henderson wrote:
On 2009-06-01, Steven Surdock <ssurd...@engineered-net.com> wrote: use pflow from base OS to export flows; we have nfdump and nfprofile in ports to log them, and there is a web UI "nfsen" that goes with these (not in ports yet, but it has its own installer) that you can use to make it look all pretty. http://www.ripe.net/ripe/meetings/ripe-50/presentations/ripe50-plenary-tue-nfsen-nfdump.pdf
