Personally I can't recommend any cos I do my own work but ones I have heard are OK are James Tennant (Okehampton), Vanstones (just over the border in Launceston) and Tredown (near Holsworthy).
Of course these could all be miles from you what with Devon being the biggest county
Depends which part of Devon. I'm guessing that Devon 4x4 is probably the best known one in South Molton.
There is a good one in Taunton that I use, Country Rovers. I'm happy to recommend them.
It may help if you give a better general location tho...