Bike rims at good prices from starbike.com
The rims are, besides the tyres, hubs, spokes and nipples an integral part of bicycle wheels. The materials used for bicycle rims have changed over the years. Nowadays Aluminium dominates the market due to its light weight and good price/performance ratio.
In professional cycling including triathlon and time trial, carbon rims are being used as well, specifically for high profile aero rims. Carbon rims are lighter than Aluminium rims, but their production is quite expensive, especially carbon rims for clincher tyres.
Aside from regular rims for rim brakes there are also disc-specific rims for disc brakes, which don't have brake surfaces on their sidewalls, which results in a lower weight and/or higher strength.
Another distinction is the tyre compatibility. There are rims for clincher tyres, tubular tyres (which are glued onto the rim) and tubeless rims for tubeless tyres. Tubular road rims became popular again because many carbon clincher rims can't handle high tyre pressures.