leethebard The Sodastream machine makes great seltzer . It's easy and fun, and you can make healthy drinks using fruit juices. I like many of their sodas, too, especially the diet ones!
Their syrups are good, but they charge far too much for the CO2. There are instructions on how to hook up a sodastream to far less expensive CO2 cartridges, reducing the price per bottle considerably.
Speaking of bottles, that's another problem with the device, especially for people without dishwashers; it is nigh impossible to thoroughly clean those things by hand.