The Tenth Doctor and Rose

The Tenth Doctor and Rose were a power couple, nearly inseparable until literally forced apart by being in different dimensions. All evidence indicates that David Tennant and Billie Piper got along quite well, but so far, their schedules have only enabled them to reunite for one boxed set. This series was also the one that introduced Torchwood, spinning off the larger Doctor Who universe, and brought back Sarah Jane, tying the show firmly to the classic series and setting up yet another spin-off.