I do this all the time - hey! cool! cardoons! Wow! Purslane! Black salsify! I buy a bunch of stuff, and then try to figure out what I'm going to do with them.
I find I regularly turn to 4 cookbooks in this situation (plus my recipe files, Every once in a while, NYT and LA Times have great features focusing on one obscure vegetable, so I save the recipes, and wait for the veggies to show up)
"Chez Panisse Vegetables"
Faith Willinger, "Red, White, and Greens"
Alfred Portale, "12 Seasons"
Suzanne Goin, "Sunday Suppers at Lucques"
Any other recommendations? I see that "Vegetable Harvest" is this month's cookbook - would people consider it a worthwhile addition?