Here are a few big ones:
Vit D - it's the magic bullet for most things: mood, immune, cell function yadda yadda. Human beings spent most of their evolution getting upwards of 20,000IU from sun exposure, but now live inside and get none. In terms of supplements I consider it as important as any macro nutrient
Fish oil - Carlson's is a good choice. You get Vit D, A and omega 3 in the same package. Tastes pretty great, too
Magnesium: Supposedly void from modern, over-farmed topsoil.
K2 - directs calcium to bones and teeth and away from arteries. Very good idea to take some extra, especially if you've been punishing your teeth by eating grain.