I think that many agents have specific guidelines for what they want to see in a query
package. For my own amusement, I spent a half-hour searching for guidelines for agents whose names I recognized. A few I couldn't find a Web site for (but they might be in Jeff Herman's book, for example), but I found most of them, and they're all reasonably specific:
Donald Maass: Alternately, you may wish to send your query letter by snail mail. We respond to every posted query that we receive. You may include the first five pages of your manuscript and a short outline, if available. Be sure to enclose a self-addressed stamped envelope (SASE) for our reply.
Richard Curtis: To submit your material, send the following: (1) A query letter outlining your professional experience. (2) One or two sample chapters of your book.(3) A self-addressed stamped envelope in order to receive a reply and sufficient postage for the return of your material if you would like it sent back to you.
Ethan Ellenberg: For fiction, please submit a synopsis, the first three chapters (approximately 50 to 100 pages) and a SASE (self-addressed stamped envelope) via postal mail.
Sanford J. Greenburger: Please submit a query letter, the first three chapters of the manuscript, a synopsis of the work, a brief bio or resume, and a stamped self-addressed envelope for reply.
Writer's House: Please send us a query letter of no more than two pages, which includes your credentials, an explanation of what makes your book unique and special, and a synopsis. Also, please include a self-addressed-stamped-envelope for our reply, which generally takes six to eight weeks.
Natash Kern: Your submission package MUST include the following if you wish to have your work considered for representation: Include a cover letter that includes a 1-2 page overview of your book.. The genre of your manuscript (inspirational romance; medical thriller etc) An estimated length or word count A one-paragraph bio and previous publishing or writing credits (if any) Your name, address, phone/fax numbers, and email address Let us know if it is a multiple submission (we do accept them). A 3-5-page synopsis of your book that must include the ending . The first 3 chapters (up to 75 pages) of your manuscript When sending a query by regular mail, include an SASE (a self-addressed stamped envelope) for our reply. We accept queries only from residents of the U.S. or Canada.
Richard Henshaw: For Fiction we like to take a look at a query letter, short synopsis and the first fifty pages. For Non-fiction we prefer a proposal. ALWAYS include a SASE (self-addressed, stamped envelope) if you would like a response.
Sternig & Byrne Literary Agency: I prefer brief query letters for the initial contact. If the project suits my current needs and interests, I may request fiction partials (the first 20-30 pages, a detailed synopsis, author's bio/writing credits and SASE)
Trident Media: To submit a manuscript or proposal, please send your query letter to one of our agents. Guidelines for your fiction submission: Paragraph about yourself, plot synopsis, previous publishing history (if any), contasct information (address, phone, fax, and email address).
Scovil Chichak Galen Literary Agency : Begin with a query letter describing your project, background, and credentials, which you may send by mail or e-mail. If you wish to receive a hard copy reply you must include a self-addressed, stamped envelope. For this first contact, nothing should be enclosed with the letter; don’t send any sample material until we advise you that we’d like to see it.
JABberwocky Literary Agency: We only accept unsolicited queries by mail accompanied by a self-addressed stamped envelope (SASE) or, for international queries, an international reply coupon (IRC) if US postage is unavailable. WE DO NOT ACCEPT QUERIES BY PHONE, BY FAX, OR BY E-MAIL. Furthermore, DO NOT SEND ANY MANUSCRIPT MATERIAL UNLESS REQUESTED. A brief one to three-page synopsis can be included with your query, but is in no way required.
Spectrum Literary Agency: Anyone interested in representation must send a query letter* with a return stamped (not metered ), self-addressed envelope to: XXXXX The letter should describe your book briefly and include publishing credits and background information or qualifications relating to your work, if any.