Paul Caron has a very useful list here. Interestingly, almost none of these programs existing when I was on the teaching market 13 years ago, though I somehow managed to procure a one-year grant to be a research fellow at Columbia. FWIW, of the five entry-level professors George Mason has hired so far this year, four have served as either post-J.D. research fellows or visiting assistant professors.
Fellowships for Aspiring Law Professors: