One of my most prized travel possessions is an inflatable travel pillow similar to the one above. (I can't find the exact model online as I bought it in Japan.) It only takes a few seconds to inflate, keeps my head from bobbing around during sleep and most importantly, folds completely flat when not in use. The cover is also removeable and machine-washable, so I can get those airplane germs off of it after each use.
I think it's pretty much the perfect design--it's comfortable, cleanable and portable--but a company called Designs in Progress has developed a competing product, their new Embrace Sleep Collar Travel Pillow, made from memory foam:
Personally I'm not crazy about the aesthetic, as it looks like something you use to restrain Hannibal Lecter, and it seems like it would get hot without that front opening that the U-shaped variety has. The Embrace is designed to encircle your neck completely to prevent forward head-bobbing, but I've found the U-shaped variety also precludes that by keeping your head more or less comfortably immobile. Lastly, as malleable as memory foam is, it won't fold as flat as the inflatable kind.
However, I should point out that I've never actually used the Embrace, these are just my impressions based on seeing it. What do you think, would you try this thing out?