These are wonderful 3-year stipends from the National Science Foundation (NSF) that come complete with additional funds to support grad student research. For other funding opportunities from NSF, check out their Funding for Graduate Students website.
These generous awards are similar in size to those offered for NSF graduate fellows, but these HHMI awards are generally made to grad students working in areas of biology with direct applications to human health.
Many professional societies offer (generally small) grants to support graduate student research in relevant fields. Information about these awards is usually available either in the back of the journal published by each society or on the website maintained by the society.