Here's one good resource:
The Definitive Guide to Primal Supplementation
I am personally partial to probiotics and digestive enzymes.
Here are a couple of useful forum threads about probiotics:
And here is the definitive thread, to date, about enzymes:
Regarding your B-12 supplement, be sure to take a sublingual, because this is absorbed much more effectively than those that have to pass through the digestive system. The methylcobalamin form of B-12 is supposed to be the best; here's the one I use:
Taking a good-quality multivitamin would also be a good idea... you can cover a lot of nutritional bases easily that way.