I second Express Park, we used them the last 2 times we flew and they were good. (south lot, I think) the van picks you up and drops off right at your parking spot so it's pretty curb-to-curb. I believe with that coupon code its about the cheapest place to park too.
the other place we used is Winner Airport parking. little more expensive but it's a valet service so they drive you to the airport in your own car if you have room for the driver and, if you pay a little extra, you can leave straight from the airport. there's usually a coupon code at longtermparking.com or something like that. depends on how long you're going to be gone whether it makes sense to use the valet or Express Park. (or use a car service instead for that matter) we used Winner at least twice and my parents and in-laws used at least once and all positive reviews
ETA: also remember there's an 18% parking tax in philly, so add that to whatever rate you find unless they state the rate includes taxes and fees. so the express park coupon is 6.75 + the 18% tax for a total of $7.97 per day.