If you're serious about time trials or triathlons, and are looking for a take-no-prisoners aerodynamic edge, seriously consider the Mavic Cosmic CXR 80 Carbon Tubular Front Wheel. It's constructed of carbon fiber with a 3K weave, with an 80mm rim depth for real slice-through-the-wind advantage. You get an exceptionally stiff wheel whose aerodynamic advantage outweighs the extra weight from the rim's depth. Mavic's carbon-bodied hubs have aluminum flanges and contain QRM+ cartridge bearings. These are double-sealed bearings and are made to a tight tolerance for high rolling efficiency; they're micro-adjustable to ensure none of your watts go to waste. Sixteen bladed, straight-pull, steel spokes lace the rims to the hubs in a radial pattern.
Furthermore, the CXR 80 front wheel includes a 700x23c Yksion tubular tire, making it one of the few aero wheels on the market that are designed for a specific tire.