Right now Crutchfield is running a sale on the previous model Polk speakers:
RTi38 = $250/pr
CSi30 = $150
CSi40 = $300
f/x 300i = $250/pr
PSW650 = $500
Of course you might also have heard they are giving away a free Polk PSW202 powered subwoofer with the purchase of Polk speakers of $500 or more.
I know some people have gotten better deals at Circuit City on blowout sales, myself included (RTi150s for $500pr!) but a lot of CC stores are sold out by now and this may be your last chance, short of ebay, of picking up those timbre-matched RTi center/surrounds you wanted to go along with your RTi70's or RTi100, etc... :)