I generally don't like the idea of taking supplements, because I feel like I should be getting enough vitamins and nutrients from the food I eat. However, I realize that I have no way of really insuring this, and I realize that I live in New England where vitamin D deficiency is rampant. So I decided to scope out the offerings at my local Whole Foods for a vitamin I can try.
There were tons of options - just plain multivitamins, vitamins with weird wheatgrass and mushroom extracts, raw vitamins, and plenty of "vegan" multis. Why vegan in scare quotes? Because most of them didn't turn out to be vegan once I checked the label.
For example, Raw One For Women. See the little picture to the left? It says VEGAN on the label, so I figured it would be free of animal products. I flipped over to the label and found that it contains vitamin D3.
If you don't know, vitamin D3 (cholecalciferol) is derived from animals, usually sheep's wool. This is the type of vitamin D that we humans produce when our skin is exposed to UV rays. It's also why we tend to be vitamin D deficient up north here when there's little sunlight all winter long.
Vitamin D2 (ergocalciferol) is the vegan option of vitamin D, derived from plant or fungal sources.
So keep your eyes open when you're shopping for truly vegan vitamins! Your best bet is to shop online at a trusted source like Cosmo's Vegan Shoppe or Pangea Vegan Store. But if you have to shop at the grocery store, read the labels and don't buy anything that says D3 or cholecalciferol.
For more information on vitamin D, I recommend the wikipedia page.