That said, I did find a few pieces of interest. RFPs seem to be a highly controversial topic, with some authors detailing how to create the perfect RFP while others recommend not using one at all. In "How to Find, Evaluate & Hire an Adertising Agency" from agencyfinder.com, it's argued that companies should use an RFI (request for information) rather than an RFP (request for proposal), which is largely a matter of semantics; the important point is to gather specific information from each agency on your "intermediate" list to help you narrow your list down to those agencies you want to invite for presentations. Beyond that however, this article makes some good points about looking for pertinent experience and taking a tour of the agency before making a final decision.
On the pro-RFP side, in "Details, Details: Writing an RFP" from Direct magazine, Katie Muldoon outlines some of the important information to ask for in an RFP, and Kevin Labick at MarketingProfs does the same here; both articles are helpful, although neither provides a formal outline.
On the anti-RFP side are Alison Glander's "Drowning in RFPs" from Promo magazine, and "Why RFP's (sic) Are A Bad Idea" from the Business of Business Marketing blog. Glander argues not so much against RFPs in general as against bad RFPs, particularly those that result in either no business for any agency or in a much smaller project than initially indicated. She provides an excellent perspective on what makes for a good RFP from the agency perspective. The blog piece is more directly dismissive of RFPs entirely, although the author acknowledges the need to ask questions of agencies regarding "their position, methodology, resources or credentials" as well as references -- which, to me, is the point of an RFP.
The bottom line is that whether you call it an RFP, an RFI, or something completely different, a well-crafted document -- one that provides enough information about your company and your objectives to enable an agency to determine if they can provide value, and that respects their time by avoiding excessive, unnecessary or intrusive questions -- helps to clarify your agency evaluation process and to establish a relationship, with the right agency, on a positive note.