I agree completely - the 135mm f2L is magical. Can be a bit long in the studio, but produces excellent images - focuses instantly, can produce very shallow depth of field.
Oh, and it is surprisingly inexpensive...
The standard L lens to get after the 70-200 is the 24-70mm f2.8L. It's a fine lens, and probably the lens I use most, but it's not quite as magical as the 135mm
And it is not cheap, either. Still, the 24-70 would be the sensible choice.
My suggestion would be to buy the 135mm f2L, and put any change leftover towards buying a 24-70mm. Christmas money doesn't have to be spent sensibly!