Does anyone have a good online source where you can buy dates in bulk?

I like Nuts.com.

Flying Disc Ranch in California. Lovely dates.

Take a look at this list: http://mideastfood.about.com/od/pantryessentials/tp/onlinestores.htm

However, have you checked to see if there are any Middle Eastern stores near your home? If you live in a city, you are sure to have some good resources nearby. I buy my dates at a Persian market and have never had better.