chesser james do a good job (yes, really...) but that's because only one bloke does it there - part time. He's a really sound bloke. Called Pete the wheel builder.
I've also had good service from 18bikes, by far the best shop for MTB in striking distance of sheffield. Though they only sell bespoke frame build ups they are happy to work on less bling gear... they've sorted my marin out just fine! The waiting time for service is usually no more than 5 days.... and it's not expensive for labour.