I have the arm warmers from Pearl Izumi, they are nice, but a bit pricey for a tube of fabric, essentially. I couldn't stomach paying 35 bucks for knee warmers, so i bought the performance ones. admittedly, not as nice, but money doesn't grow on trees, right?
The pearl arm warmers are pretty nice, very warm. a good combo for 50-60 degrees, I've found, is a jersey , wind vest and the arm warmers. just a suggestion.