Dougal, you may consider looking into Velomax. I don't think I've ever ridden a pair, but they're developing an increasingly loyal following in the enthusiast and racing worlds alike. Their mid-range centerpiece, the Ascent II, retails for a little over $600, and is apparently fantastic -- great ride quality, reliable, light -- the usual stuff.
The slightly heavier, more budget-oriented Circuit Comps can be found for under $400, if you look hard enough. They're also a favorite in their price category.
Check out the
Velomax website.
Also, I know a lot of guys riding modest Ritchey wheelsets; mid-range and lower-end Ritchey stuff tends to be solid and reliable, if not super sexy or super light.
At the same time, it's worth noting that the Campy Eurus and and cheaper Proton are pretty hard to find too much criticism for; people seem to love them.
My basic wheelset is the no-longer-available Shimano WH-6500, a paired-spoke Ultegra level design from a few years back. User satisfaction is mixed, but I've found them extremely durable, and nicely aero, if not the lightest wheels around. They retailed for over $600, but there are old over-stocks and used ones floating around for well under $300 by now, I bet.
Good luck!
