If your broadband is ADSL via the phone line (as opposed to NTL or Telewest "Cable"), then you want a combined "Router/ADSL Modem".
Having established that, you then need to decide whether you want to connect to it "wirelessly" with one or more computers (or whether in the future you may want to). The additional cost of a Wireless Router over a Wired-only one is much less than the cost of having to buy a separate "Wireless Access Point" later in order to upgrade the network.
Hi, I have a BT Voyager 2100, this is a wireless modem/router with 4 ethernet ports. I use the ethernet ports for my 2 desktops (even though one has built in wireless) and wireless for my two laptops. All work very well, no complaints. The kit costs me £99.99 and included a wireless card for a laptop and one for a desktop - I sold the desktop card and got £25 of my costs back!. The rub - not seen a £99.99 deal since!!!