Multi-vitamins aren't that useful on low carb; I tracked when I first started Atkins, and made the RDA for everything but D without effort. But Vitamin D3 is a good place to start; most people are too low.

Vitamin D Council

To target which vitamins to take, there's an excellent book:

The Mood Cure

which makes the excellent point that sometimes we need amino acids and actual nutrients as well as vitamins.

For instance, I take niacin in large doses routinely, which helps me in a lot of ways. But while it works for me, it might not work for you.

And my constant hunger and cravings was helped by chromium picolinate. You finish a bottle and see how you feel.

But this is very individual and one must be willing to monitor their own feedback.