I am not a huge supplement guy but there are a couple supplements that I take year round. I get all my supplements at Costco, N2bm.com and amazon.com
1. Fish/krill oil - costco
2. A good quality multivitamin - n2bm.com
3. A high quality whey isolate powder - n2bm.com
4. digestive health supplements - greens powder, psyllium husk, probiotics and digestive enzymes - costco and amazon.com
The most important supplements are fish oil and a good quality multi vitamin.
The biggest thing to look for when shopping for a multivitamin is what form the minerals are in. Most supplement companies use mineral oxides in their multi vitamin products because they are cheap. The problem with that is they only have a 2-4% absorption rate. Take magnesium or zinc as an example. Most multivitamins will have the forms of 'magnesium oxide and zinc oxide' listed.
What you want are amino acid chelates. You want to see 'magnesium amino acid chelate and zinc amino acid chelate'.
Check ruthless 3d from n2bm.com. It only contains amino acid chelated minerals. It also has higher dosages of B vitamins, vitamin C and vitamin E. It was formulated with the hard training athlete in mind.