AGP cards are starting to appear and are almost certainly worth having - but I'd like to wait for a while before I recommend one. You also need a new motherboard with an AGP socket, of course. The Creative Labs 3D Blaster Voodoo 2 is quite new but has already made friends. It uses the new 3Dfx Voodoo 2 chips and is extremely fast, especially when you use two boards together. However, it isn't any faster than the other boards using Voodoo 2 so shop around (i.e. try Diamond, Orchid or a whitebox board).
Cards based on the Intel 740 are sure to appear in the UK soon (e.g. Real3D StarFighter). This excellent Intel chip-set (bought-in from Real 3D) has the best quality 3D rendering I've seen to date on a PC. It isn't as fast as the Voodoo 2 - which beats the rest by a good margin, but it is faster than most existing boards. You choose: speed or quality.