If you're like me and are constantly asking yourself "Where do I know that actor from?" while watching TV, then the 'I Spy A Famous Face' Tumblr is just for you.

This ingenious photo blog spots famous celebrities in guest star appearances on television shows other than their own. Some of the great finds include 'Grey's Anatomy' star Ellen Pompeo as a guest star on 'Friends,' as well as Anna Faris, the Disney Channel's Dylan and Cole Sprouse and 'House' star Hugh Laurie.

The 'I Spy A Famous Face' Tumblr also delves into sitcoms like 'How I Met Your Mother,' 'Vampire Diaries,' 'Glee' and 'One Tree Hill' to search for famous faces making guest appearances on some of TV's most popular shows. Check it out and see if your favorites made the list.