Buddy Eleazer has just posted a great summary of the most popular bean bags on the market on his Chobe Safari blog. This is a great resource if you are in the market for a bean bag.
My own personal preference is the Kinesis Safari Sack. I have a few dozen that I have for my safari travelers that are always in Tanzania waiting for me. We fill them up with red beans that we purchase at a local market, and the guides empty out the bean bags at the end of our safari and take them home with them to eat. I don't want to have beans sitting around rotting in the bean bags. If you are traveling and do not anticipate having access to beans, I highly recommend purchasing the Kinesis Safari Sack that is prefilled with buckwheat. It is a lightweight option, and the buckwheat is an excellent filler.