I can think of a few memorable voice acting performances that stood out from the rest.  But few can compare to this one. Armin Shimerman, who is also known as Quark in Star Trek Deep Space Nine, delivered a performance to be remembered. I mean who can forget these :
 

Definitely one of my favourite characters of all time. Loved his performance on the audio logs. And there are so many great quotes, given that he's all over both BioShock games. Even heard him in the new single-player DLC for BS 2.
 
I'm pretty confident that Infinite will be incredible, but I hope they can come up with a character as interesting as Ryan.