In the latest sign that nearly every U.S. airline has given up on making its customers remotely happy, JetBlue is now going to charge $7 for a blanket and pillow. I've got a better idea: either fly on Continental (where they're still free) or buy your own much nicer kit and keep it.
In the past I reviewed the great Pacn'Nap flight kit pictured here and it does a great job of solving both issues at once. It contains an inflatable pillow and a fleece blanket and it feels much nicer than what you're going to get on any plane in coach. You can get a very similar double-duty item from eBags from a different manufacturer: Foldable Blanket Pillow/Lumbar Cushion
If you don't care about the blanket and just want a pillow, you sure aren't hurting for choices. At REI.com for example there are 25 to choose from and at Backcountry.com there are even more.
Judging by what you see in airports and luggage stores, a lot of people go for the horseshoe-shaped pillows that conform to the neck, but they turn into useless baggage once you deplane. I prefer the idea of a regular-shaped pillow like this Comfort Plus pillow from Magellans because that can also be used in other circumstances, including when you need something under your butt for hard train/bus seats, watching a ball game, a hostel stay, whatever.