It really bugs me when I recognize an actor in movies, or TV, and can't place where from.
The solution is invariably found on IMDB and their new (for us outside the US) iPhone application makes it easy.
Search for titles, cast, crew and more with massive amounts of related info on every title. I also like the links to reviews outside IMDB's database and to Amazon.
Its an impressive app that should be on your phone.
(seen displaying my favourite ever movie "Local Hero")