Just a quick post about two technologies that are on the way out IMHO:
– CRT monitors are being replaced by LCDs which are very light and, more importantly, take up far less desk space. Also it seems to me that LCDs tend to be sharper. The price of LCDs has also been dropping significantly, so if you are looking to upgrade/buy a new system I’d definitely recommend buying LCD.
– Inkjet printers are slow and the cartridges are prone to drying out if not used frequently. B&W Laser printers have come down in price very nicely and are so fast; they can spit out a page in the time it takes an inkjet to do a couple lines. If you print a lot of text, a laser printer is a must. Color laser printers are still expensive, but will likely be reasonable in the not too distant future.
[Update October 18, 2008: You can add FireWire to the list too.]