Epicurious has a sweet little applet that you just might find useful: an interactive Peak Season Map. It's simple to use, just select a state and a month to display a list of produce that is likely to be available at farmer's markets. (I'm going to check when I go to the market this weekend and see how the list matches up to reality. It says there should still be rhubarb and I haven't seen any in weeks. Then again, maybe it is still growing on the other side of the mountains.)
Each type of produce has links to a description of the ingredient and recipes, some also have preparation and shopping tips. It looks like it could be a handy thing to have bookmarked, particularly when planning for the future or sharing recipes with friends in other places, or to reassure yourself that berry season starts next month and that's really not so long to wait.