Sci-Fi Fan:
Moffat does have two potential established companions to make use of. He created River Song (Alex Kingston) in the Library episodes who is clearly a future companion of the Doctor. Also, Sally Sparrow from Blink would make a fantastic companion as she seemed to understand the complexities of the wibbly wobbly timey wimey stuff.
I fully expect RTD and SM to work together during the 2009 specials so that the new series kicks off to a flying start.
Of course, there's always David Morrissey who seems to be very Doctor-like in this year's Christmas special.