Layout my tiles for me
Python 2, 151 149 bytes

from random import*
W,H,N=input()
L='x'*W
exec"M='';exec'M+=sample(set(map(chr,range(65,65+N)))-{L[len(M)],M[-1:]},1)[0];'*W;L=M;print' '.join(L);"*H


Takes input comma-separated via STDIN, e.g. 10, 10, 2.