Rita Cosby and Diane Neal

---

Tobey Maguire and Topher Grace

Both appeared in Spider-man 3, with Tobey as Spider-man and Topher as Venom (the "anti-Spider-man").  It wouldn't surprise me if part of the reasoning behind Topher being cast for the part was due to their resemblance.  I remember when the trailer for the original Spider-man came out I had thought to myself back then, "Hey, that guy from That 70's Show is playing Spider-man!"  So confused.  :]
 

Alright, now your turn:
Tobey or Topher?

---

Brett Favre and Casey Blake

One plays professional football, the other plays professional baseball.

---

Russell Brand and Captain Jack Sparrow

 

One's a British guy whose brand of comedy I just don't get, while the other one's the skipper of the Black Pearl.

(p.s., Johnny Depp rules!!!)

 
 
 
 

---

Keira Knightley and Kate Winslett
 
 

I'm guessing this one's probably a stretch to most people, but I get them mixed up all the time -- maybe it had to do with all the "k"s in their names.  I suppose I can try to associate Kate with Titanic, but then Keira had to go and do the Pirates of the Caribbean trilogy which obviously has boats in it, too!

A bit of trivia I just found out today was that Keira appeared on Star War's Episode 1: The Phantom Menace.  She apparently was the one playing the Queen Amidala look-alike in the movie. Oh, and imdb states that Sophia Coppolla was in it, too!  -- um, okay I'm getting sidetracked.

But anyway, there you go; my list of nominees for the "Separated-at-birth" category.  :)