"I've seen fake gods and bad gods and demigods and would-be gods; out of all that, out of that whole pantheon, if I believe in one thing...just one thing...I believe in her." ~The Tenth Doctor speaking about Rose; Doctor Who, The Satan Pit (S2E9).
This is not only one of my favorite quotes from Doctor Who, it is one of my favorite quotes of all time. The passion David Tennant uses while speaking about Rose (while in character of course), is the passion of a man in love. Of course you never see David Tennant's version of the Doctor actually tell Rose that he loves her, but it is implied (why else would he burn up a sun just to say goodbye and why would he give her another version of himself?).
This quote basically proves that it doesn't matter who we believe in, as long as we believe in someone (or in a lot of peoples' cases, something). The Doctor believes in Rose and Rose believes in the Doctor. This quote makes me happy and sad at the same time, but more on that at a later date.