The first corn begins trickling into markets in the early spring from the desert growing areas, but starting in mid- to late-June, the flood really begins. Always one of the most popular farmers market items, it is grown in Orange County and the Valley and should be around for the rest of the summer.
Most of the corn you'll find is white (that's just a regional preference in Southern California, and, despite what you may have heard, it's not necessarily sweeter than yellow). And most of the corn is from one of the newer varieties that hold on to their sugar longer than the ears of yore. While those older corn varieties tended to go starchy in a matter of hours, these will taste sweet for a couple of days. On the other hand, they tend to have a little less "corny" flavor and, because of their thick skins, the kernels usually aren't as creamy.
How to choose: Ears should be well filled out (check the tips of the ears to make sure there are kernels), and make sure the silk is still soft, not dried out. Don't shuck the whole ear before buying, though; it makes the farmers really cranky.
How to store: Corn should be refrigerated, tightly wrapped.
How to prepare: If you haven't already tried grilled corn, you really need to. Soak the unshucked ears in water to cover for at least 30 minutes. Then toss them on the grill. Turn every 5 minutes or so until the corn is golden; it'll take about 20 to 25 minutes total. Shuck them before serving and the silks will come off with the husks.