I just found foodtimeline.org, an interesting and fun resource (through Mona N.‘s friendfeed page). You can find out when different foods first appeared in history. But it also contains or links to the old recipes used at different times (or to hypotheses when it’s too far back to know) like in the 16th c. english “Booke of Cokerye” or the dutch 16th c. “Cocboeck” of Carolus Battus.
Also I found out that oldest recorded reference to one of my favorite vegetables, the Eggplant (Μελιτζάνες, Melenzane, Solanum melongena) is chinese (interesting since I’ll be visiting China soon, though not for the eggplants). It appears in the ‘Qi Min Yao Shu‘, an ancient chinese agricultural text of the 6th century AD, says wikipedia’s eggplant entry and the Vegetable Travelers entry.