I've been seeing this around the web for the past few days and figured I'd put it up here as it's really nice looking as well as very informative. Aside from the obvious meaning for the gardener, they're also helpful for non-gardeners that like to keep their diet tied to the seasons. There are also similar charts for fruits and herbs. Prints are available for sale by the creators at their web site:
Chasing Delicious
Sorry it has taken over a year to post, life has a way of interceding.