There's lots to choose from at the £6-800 mark. The Kona Jake, Spesh Tricross and Focus Mares all spring to mind. I have a Jake which is the least flashy and worst specced of the lot, but it does the job fine! Celia has a Jake the Snake which is very similar but a bit lighter. Nouveau has a singlespeed Tricross and a Jake The Snake and rates them both, although he rides the singlespeed more, for perverse reasons of his own. Dylan likes his Dolan too.
Second hand is a good way to go, that's how I got mine and Celia's. If you want it for commuting, bear in mind that some of the racier frames don't have bottle bosses or mudguard eyelets.
Race season's coming up soon, get your bike sorted and we'll have to go out on some training rides!