Do you like Doctor Who? Sherlock? Things that are awesome? Then you simple must watch Wholock, a fan-made mash-up so amazing that you will swear that someone must actually have filmed Benedict Cumberbatch standing in the TARDIS, acting opposite Matt Smith.
There are a few shots where the characters' lines of sight don't exactly match-up, but the editing is so amazing, both in the chosen dialogue and the composition of Cumberbatch into the Doctor Who footage, that it seems almost petty to point out such a small problem in something otherwise so flawlessly executed. Sorry, other Doctor Who/Sherlock masher-uppers, the bar has just been raised.
It's also worth noting that the sexual tension between the two characters is, of course, palpable. Somehow I doubt that was entirely an unintended effect.