I was just reading mic9aels site after a couple of postings of his, and saw the mention of the large block of shrimp averaging around $7/lb.
Never really thought of posting this before, but at many of the asian markets in the area, I've been able to routinely find $5/lb shrimp of all sizes, and in 1 or 2 lb bags. Also of course there is good squid on a good price, and I then also often buy cilantro, basil, etc from them as well. The basil at Bangkok 54 in Arlington is outrageously cheap, plentiful and good!
Now that I'm in the burbs, I've found a decent market on Maple, near Nutley in Vienna.
Oh, and a bigger score than that - the jasmine rice! Huge bags for $2 or $5, puts anything at safeway to shame.