Not sure what qualifies as a "good dentist" but I go to the one on Waterloo Road down the Elephant and Castle end which has cleaned up my teeth nicely.
It is a private dentist though so is not the cheapest.
Best dentist in s.e.1. is Charles Ng near the library in the Old Kent Road, near east street, he does National health too, a bit of a rarity these days......he has managed to preserve my old gnashers! despite me having a fear of I.Pullem and co! not a modern surgery full of flashy waiting rooms...
If you are looking for NHS Mr Ooi in Kennington Road is fine. There is a nice lady who works there three days a week. Bit out the area though in Kennington, just beyond Kennington Cross, about midway between Pizza Express and Daniel Cobb.
EJN Chater gets my vote too. It's brilliantly oldee stylee in there, although I've noticed the street entrance has changed recently, and he's a good dentist. Doesn't try and sell you loads of expensive treatment that you don't need.
Corner of Borough High Street and Trinity Street.