I'd set myself a budget of up to £700 or a new pair of aero wheels for my road bike, to replace the American Classic 38's that came with the bike four years ago. I use conventional braking (alloy rims) and want a deeper aero profile of at least 50mm. It turns out that there aren't many suitable wheels that retail around this price, but there are bargains to be had.
The target brands started off as Zipp, Fast Forward and Fulcrum, with others being considered as my research continued. Here's the short-list:
Most of these wheels retail at £1000 or more, but are on offer at around the £700 mark. At 1620g the 3T Accelero wheelset is very light, but historically people have complained about it being noisy. The Halo Carbaura wheels are nice, but at 1950g are very much on the heavy side.
The online prices of all of these wheels are very tempting, but I'd strongly recommend heading down to your favourite local bike store and seeing what they've got. The store that sponsors my bike club was able to sell me a good quality second-hand set of Zipp 60's, saving me a few hundred pounds!