NonProfit Storm provides an up-to-date and completely searchable list of the United States Internal Revenue Service (IRS) 501c3 Non-profit organizations. Learn more about non-profits from the official US IRS Charities and Non-profits page.
If you're interested in knowing about contributions and whether those contributions will be tax-deductible, you can search this list. Check out the line labelled "DEDUCTIBILITY" and look for the term: "Contributions Are Deductible," next to it. Also, check out the IRS page on Charitable Contributions. You may also confirm an organization's status by calling the IRS (toll-free) at 1-877-829-5500.