Which is the most early type star with a planet discovered by radial velocity method?
HD 103774 b, detected by radial velocity, orbits a star of spectral type F5V according to The Extrasolar Planet Encyclopeadia.

HD 102956 b, detected by radial velocity, orbits a spectral type A subgiant, the star of the "earliest" type harboring a planet detected by radial velocity, I could find (as of May 2014).

The entry for
Kepler-88 c around a spectral type B star (according to the catalog as of May 2014) appears to be incorrect, or encodes something else, the star should be classified as spectral type G6V.