It's the 21st century and we all like our electronic gadgets. Speedometers have been a part of cycling ever since the early but the bike computers of today can do a whole load more than just tell you how fast you're riding.
How far into the realms of technology you wish to go is up to you. If you just want a simple speedometer computer there are plenty of very affordable ones to choose from. The price of GPS enabled computers has shot down in the past few years and chances are that anyone looking for a decent bike computer will be looking for one with GPS functionality in it even if it's just a GPS logging computer rather than a full-n Satnav style navigational unit. Training aids such as heart rate monitors are invaluable if you're serious about your fitness regime and progress. A relative newcomer to the world of cycling tech gadgetry are sports action cameras. Small HD cameras that can be mounted on the bike or on your person - usually helmet-mounted - for recording your cycling adventures and misadventures from a first person perspective.