The edinburgh bike coop in Newcastle is good. I assume there is actually one in Edinburgh.
Big names are always a good if predictable bet.
Specialised, Trek, Kona, GT, Giant.
Try some mens bikes too. There isn't a huge difference in the geometry but much more choice. Often by fitting a shirter stem and ladies saddle they can be converted. Most people fit shorter stem immediately anyway as they think they handle better (I often do).
Bikeradar has some good info (as well as reviews) and I would suggest looking in a newsagent and picking up a few magazines if they have reviews in. What MTB is good for that.
Have a look at some, find the links and post them back here. People will probably give you advice on which ones are best.
I would look at frame, fork and wheels as being the most important as they are most expensive to replace.