As far as I am aware, the Foundation Directory is the first real database established for grant research. This extensive database has been in existence for years and offers many grant writing professionals their first introduction to the art of grant research and writing. The Foundation Directory is an offering of the Foundation Center that also offers a variety of grant writing courses.
The Foundation Directory, though, is exactly what the name implies — a list of the various foundations that give funds. It concentrates more on the organizations than it does on the funds they offer. You can find the history of each organization and a great deal about their leadership and past awards, but I find other databases to be more accurate when searching for specific grant fund opportunities.
By using the Foundation Directory in conjunction with other databases, you can get a full view of a funding organization. As the oldest resource, it is not cheap to access their files. But what you can get from a Foundation Directory membership is a complete view of the funding organization you are targeting for your next ask.