*DHA* omega-3s are the most useful to your body. These can be found in algae, but other plant sources of (non-DHA) omega-3s may not be usable in your body, at least not efficiently enough to be good supplements. Omega-3s are also vitally important in your nervous system.
I know you didn't ask, but..
Vegetables, deep-green and yellow ones I believe are the best. Canned being your last choice, fresh being your first. Fruits. Strawberries are good as well as apples. Whole grain pastas. Beans; pinto beans, garbanzo beans (yum), lentils, black beans, white beans, Lima beans. Nuts, seeds.
As for vitamin supplements,...
B-12- popcorn, soymilk, breakfast cereals, or supplements. Without it you can suffer irreparable nerve and eye damage.
Vitamin D- sun exposure, rice milks.
Omega 3 fatty acids- flaxseed oil, walnuts, soybeans.
All of these can also be found in pill form as you very well know.
I think you just failed so hard I died... Why'd you go vegan?
I was a vegetarian before, so it's not a LOT of difference. I've been vegan for 5 days now, and my mate keeps nagging me to find out what I should be doing to make sure that I don't die or something. I just decided to, ok?