Great discussion going on here. It's good to get so many different points of view and different experiences here.
As a nutritionist I would absolutely reccommend omega 3 supplements. As a vegan I hate to admit it, but krill or fish oils are the best sources of omega 3s because they are long chain fats. Vegetable sources such as hemp and flax oils must be converted by your body to long chain and this process is frequently faulty in modern humans. A vegan source of long chain omega 3s is marine phytoplankton. This is also a great source of minerals and more but can be expensive. Finances allowing, the best thing to do would be to take krill oil AND marine phytoplankton plus include hemp and flax in your diet. The less deficient you are in long chain omega 3s, the better your conversion rate will be from vegetable sources. (some phytoplankton products on the market contain very little actual phytoplankton - a good brand is Ocean's Alive Marine Phytoplankton - I am not financially affiliated with this company in any way).
Other great mood food is cacao (raw chocolate). Google search for info and suppliers.
Vitamin D from sun exposure is essential. Please don't use toxic sunscreens, just be sensible in the sun and build up your exposure times to morning and evening sun slowly so you never burn.
Exercise really helps too. If you excercise outdoors you can get some sunlight vitamin D at the same time.
Lightboxes for SAD.
5-htp is also great but don't take in combination with antidepressants for safety reasons.
Stack the odds in your favour by doing all of the above
Peace
Sunangel