He does an out-standing Gruden and if you close your eyes, a pretty good Stephen A. Smith. He also appeared on the Jim Rome radio show and it's pretty much impossible to tell him and Rome apart.
http://news.yahoo.com/video/frank-caliendos-latest-batch-impressions-223000348.html check out the first part of that video and his Gruden impersonation has been refined and is much more on point.
His Jim Rome, while very good, can be a bit of a moving target but his John Gruden is very impressive.