As far as I can tell, so far this is the best spot for grinding souls and titanite. Just equip both silver rings, shield of want and the mimic head, kill the two silver knights on the stairs and the red eyed one to the right. You can gain around 18000 souls in under 2 minutes. Very nice indeed (^^)
Also, the knights drop the complete silver knight set which is quite a nice, if you're a knight type player!