You might want to look into sodaclub.com if you drink a lot of seltzer or soda.
I've had one of their units for a couple of years now, since I heard about it here. Every couple of months or so, I order another set of C02 canisters and they have a local courier system where they put new ones on your doorstep and take away the empties. It pays to have 2 or 3 extra canisters because the delivery is cheaper.
The plain soda is very good. I enjoy it with just a twist of lime or lemon. They also sell many flavors of syrups - both with and without sugar (and you can buy syrups from lots of other places as well). My favorite is to mix up a bunch of syrup from the crystal light lemonade and have sparkling, sugar-free lemonade. ( 6 crystal-light powder cuplets go into their standard size syrup bottle - I just reuse theirs, but you can use anything you want - you use one capful of syrup per liter of soda).
Where they don't have the courier, they use parcel services, so they can get to you pretty much anywhere.