21st Century Health Care, D-1000, D3, Extra Strength, 110 Tablets

The tablets are small and easy to swallow. I also like, that they put in extra 10% at no extra cost. I take mine in the morning, because vitamin D is also known to affect daytime/nighttime rhythm. I'm perfectly happy with it, and will purchase again when it runs low. Depending on where you live, you might want to take 1-4 tablets a day - see below. 

In modern life with indoor work, most people rarely expose their skin to the sun. It is suggested, that 80% of americans (and probably the rest of the world as well) are deficient i vitamin D, with severe health damage. Most adults should supplement with at least 2000 IU per day at summertime, and at least 4000 IU at winter. 

You can buy it here