So, writing a book is tough. This is a universal fact (and if it's not a fact for you, then I hate you. Okay, maybe hate is a bit strong. How about loathe? Yeah, that's better). Getting that book published seems to be even harder. The next step, after you've edited and revised, repeated that ad nauseum, is too find an agent (unless you want to go a different route like self-publishing or directly to publishers which I know nothing about). So, I thought I'd put together some links I've found useful for this process.
The very first step when you find an agent you're interested in is to go to their website to make sure they rep what you write, are accepting submissions, and to make sure of their submission guidelines.
Literary Rambles has been absolutely INVALUABLE for me. The tons of agent spotlights are helpful and concise. The "Helpful Posts" in the right sidebar are just... well... INVALUABLE.
The Absolute Write Forums are a great place to meet writer buddies, get critiques, and find out even more information on prospective agents from people who have real experience with them.
I can't do a query blog post without mentioning QueryTracker. So much info on agents there.
The Query Shark: read every word, you guys, to help with your query writing. Same goes for The Evil Editor who is really good about critiquing every query sent.
Publishers Marketplace is another place to find agent info. Their most recent sales, their submission guidelines, and links to their websites. Some sections are for paying members only, but there's still a lot of info to be had by us poor people.
Oh and check to see if your agent of choice is on Twitter. If he/she is, then stalk, er, follow their tweets. But, for the love of all that is good and holy, do NOT pitch to them on Twitter. Unless they're doing some type of Twitter pitch contest. Maybe there is someone out there that pitched to an agent on a whim on Twitter and it actually worked out for them, but I have yet to hear that story. I've only heard agents say that this does not work.
Google... yes, Google the hell out of the agents you're interested in. Read their blogs, read every interview they've ever done.
And just to keep your spirits high and maybe spur you toward following your dream, check out the How I Got My Agent columns over at Writer's Digest. Some days I read one after another after another just to remind myself that it does happen as long as one works hard enough.
Obviously I'm not an expert at this whole thing because I am neither repped nor published (and even if I were either one of those things, it probably wouldn't make me an expert), but this all comes from spending A LOT of time investigating the process. I hope this helps and if you have any more suggestions on great places to research agents or to help with query writing, comment away!