I've listened to the voices people have linked to the wav files of but they just don't sound the way I recall. And now I don't think it was Sydney Greenstreet, but perhaps Peter Lorre's voice.
But Streakn, I thought you might have hit it on the head. Sometime in the last year I saw an old Bugs Bunny halloween cartoon that I might have remembered the voice from. I think the animation of Igor look like Peter Lorre even. I remember Bugs being locked in some castle and some monster was chasing him. I found the "Hair Raising Hare" on YouTube (with Peter Lorre character as Evil Scientist) and watched it but unfortunately he doesn't say Yes Master during the cartoon. This is going to drive me nuts until I find it. I really appreciate all the help you guys are giving me.
BTW I really liked the trailer for Igor (2008), never heard of this annimation before. They certainly said Yes Master enough times though! I'll have to see if I can find this one and watch it. Thanks for the link.