In Derby you've got;
- Samways, that stocks a wide range of kit from low end to high end, big names like specialized through to the likes of Cotic/ Charge. They are never cheap, but no more than most LBS's, and the shop staff are friendly enough most of the time, the workshop staff tend to look like they have a dog poo top lip, and treat you accordingly, but their work has always been good ime.
- Mercian Cycles, less stock but they sell Mercians and this makes them worth a visit alone. More of a roadie bias, but do MTB kit. Their wheel building is fantastic and decent chaps to boot, it's definately my shop of preference.
- The Bike Shop, seem friendly enough, but never seem to have in what I need (probably just bad luck), bit more low end than Samways.
- A couple of Halfords
- Lesuire Lakes down in Breaston which ain't far.
And if you are heading up the A6 to the Peak, you've got Stanley fearn's in Matlock.
So for a place the size of Derby, I feel pretty bike shopped up.
Edit - I think Joemarshall has come up good with that idea, but it might be worth finding out why Samways closed their shop there.