Grants.gov was built as a comprehensive source for federal funding opportunities, and I'll be the first to admit that the feature set and navigation can take a bit of getting used to. One aspect of the site that helps make it easier to find opportunities is the email notification service. Instead of searching for grants on the website, you can set it up so the grant opportunities come to you.
To sign up for the Grants.gov Grant Notification Service, use the form here and select what kind of activity your organization is seeking funding for, what kind of funding results you're interested in learning about (grants, contracts, etc), and your applicant type. Once you submit the form, you'll be enrolled to receive a daily listing of all of the new funding opportunities that match your search criteria.
The service is limited to federal funding opportunities only, which means that it will only list grants from federal agencies. Since private foundation grants are not included in the database, this service won't supplant a comprehensive grant search, but it's a great place to start.
At TheGrantHelpers.com, we have two specific services designed to help you find relevant funding sources. Consider hiring us for a Funding Opportunity Search, where we guarantee we'll find you a grant match. We also offer a free grant notification service called The Watch List, wherein we promise to contact you if we come across an opportunity that might be a match for your organization. For more information, visit our Services page or contact us.