The Rookery in Clerkenwell is nice in a charming quirky way, as is the sister hotel Hazlitt's in Soho.
For a bit more modern The Marylebone has nice rooms and is central. Also modern are the Park Plaza group, I've stayed in a couple and found the rooms and facilities very good. Pearl the restaurant is excellent.
The Chancery Court in Holborn/Covent Garden has amazing rooms and the bathrooms are good, breakfast is pretty damn good too.
The Kingsway in Covent Garden has spacious rooms that are comfortable and is in a good location.
Crowne Plaza in the City has a great Italian restaurant attached operated by Giorgio Locatelli and the rooms were good, although that was a couple of years ago.
I'll keep thinking......