Which modem should I buy?

If you don't have a modem, your best bet is to buy a 33.6Kbps modem that you can upgrade to 56Kbps. While it sounds complicated, this is very common. Just make sure when you buy a modem, you ask if it is upgradeable. Generally, there is no charge for a software upgrade from 33.6Kbps to 56Kbps modem. You will want to check and make sure the 56Kbps modem will be compatible with your ISP.