|Almost any 56k analogue dial-up modem with do. |
When I was using dial-up I had a lot of satisfaction from US Robotics modems. They were well built, reliable and reasonably cheap.
Which one you chose is largely dependent on how much you are prepared to spend. I would go for an external Modem initially as they tend to be more reliable. But that is dependent on the computer having an RS232 serial port which cannot be guaranteed these days. Other wise it is an internal PCI modem providing you have a free PCI slot in the computer.
There is a USB modem there that might be suitable as PCI is on its way out as well. It will probably be the easiest to install.