One reason why I loved Donna and the Doctor. They never were or wished to be romantically involved. Proof that there does NOT have to be "romantic tension" to make a male/female relationship intense and wonderful.
*Spoiler* If you haven't gotten that far in Doctor Who. But when I found out that he was The Face of Boe, I kind of figured it out before, but it was still a big surprise. The people of BBC really do know what they are doing.