A best bet is the
Gap Men's NY Empire State Crew Neck Sweater in Heather Gray (pictured) for $39.99 before the above coupon, $25.99 after. With $7 for shipping, that's $19 off list and the lowest total price we could find. It's available in sizes XS to XXL.
Update: Even better, coupon code "PRETTYGAP" stacks with the above code for an extra 25% off. (It excludes 1969 jeans and cords.) Together, that's by far the best percent-off discount we've seen from Gap this year.