Searching abstracts of successful proposals is a good way to help identify what sponsors consider a good proposal. Proposals awarded by federal agencies are available under the Freedom of Information Act (FOIA). Requests can be made to Principal Investigators for a copy of their successful proposal. Below are some web sites where you can find recent awards and/or abstracts of awarded proposals.
National Endowment for the Humanities (NEH) – Search on individual grant pages
National Institutes of Health (NIH) – RePORTER is an online reporting tool for NIH
National Science Foundation (NSF) - Award Data
U.S. Department of Education - Grant Award Databases
U.S. Department of Education (FIPSE)