As said by Kona TC Kathmandu is very good – friendly staff, good traditional curries as well as Nepalease menu (i’d recomend the Sea Bass Palu).
Old India (near St Nick market) has great food – and is in an old bank which is a listed building (with amazing 100% original victorian toilets), but last time i went (2yrs ago) the building needed a bit of work doing to it and i’ve not been back.
Rajmoni in Clifton near The Triangle are also good.
Best ‘out of city centre’ curry i’ve had is Tandori Nights in Staple Hill, small restraunt but really good traditional english curries and great staff.
As nickjb says – there are lots.