I agree with pbe gummi bear...
There really is no one great target area, but older homes (say 1950's-1970's tracts) are generally a better bet for finding something on a curb. Trailer parks are a good option too. However, many times now people are posting a free ad on CL...and within an hour, kettles are gone.
Also, check college towns on "move-out" day. My brother finds everything (bikes, ice chests, etc.), as he lives a few blocks away from the university. You may not find a Glen Blue this way, but you might get a sweet little 18" or SJ.