Recently, I was privileged to listen in on a teleseminar as Randy Peyser, local author of "From Crappy to Happy", interviewed literary agent Linda Langton.
I was pleased to hear that Linda is one agent who will always give feedback to an author. She prefers to receive "snail mail" queries. By the way, a proper query letter will be well-crafted, short and to the point. It should contain one paragraph on the author, and one to two paragraphs about the book.
A novel should never be queried to an agent before complete. A sample book proposal should include a chapter by chapter outline, as well as three chapters to showcase the author's writing style. It is also common and acceptable to query more than one agent at a time. Just let them know.
Linda also had an opinion on self-publishing. She opined that you're more likely to be signed by a publishing house if your self-published book has won an award, and sold a decent amount of copies.
I have my own opinions on self-publishing fiction, but more on that later.
Linda is interested in receiving queries on what is selling right now, and that includes Young Adult (YA): vampires/fantasy/magical realism (think Twilight). In non-fiction "how to" and inspirational books (like Randy's) are quite popular.
Crappy to Happy: Small Steps to Big Happiness NOW!