Like Barry, I take Vitamin D supplements in the winter (and, indeed, for much of the rest of the year too, do to my semi-nocturnal lifestyle). I do so because of the NHS recommendation in that respect.
However I agree with Helen (and her GP) that other vitamin supplements are a waste of money (and, in some circumstances, actually harmful) for most people.
To return to the original question, I buy supermarket own-brand Vitamin D tablets. They're just as good as any others.