It’s hard to find good examples of well-written research grants, so this website is wonderful. It shows examples of all sorts of NIH grants (R01, R03, R15, R21, R33, R41, R42, R43, R44, K01, K08, F31) as well as sample data sharing plans, biosketches, and reference letters.
National Institute of Allergy and Infectious Diseases. Sample Applications & More. Available in html format, but please note that the links on this page go mostly to PDF files.