ProBikeKit aficionados will know about the 24-h sale on Conti GP 4000S that brings the price down to $31 if you buy two (generally needed for two wheels), and $31 for four.  Those using the more expensive Conti Gatorskins may want to consider switching – the GP4kS is pretty tough.  (This is not the new multicolour model I mentioned previously – however, the sale may be to clear out stock for the new one.)