I finished writing my book and want to publish traditionally, now what?Congrats on finishing your novel (meaning it's squeaky and shiny, and someone other than your best friend or mom has read it). You've worked really hard and should be proud of yourself. :)
I'm not sure how much help I can give in finding an agent since I'm unagented myself, but this is what I'd do if I was in your shoes. Just know querying sucks (rejection actually is the sucky part). And even if you land your dream agent, that doesn't mean they'll be able to sell your story. So, know there will be bumps, but this is your journey. Just don't quit.
Write a Query: First thing you need a seriously awesome query. 250 words about your protag and story that'll dazzle an agent to where they want to read your book NOW, basically. Janet Reid has an excellent post to help you tweak your query. http://queryshark.blogspot.com. After it's written, you can submit to the Absolute Write forums (http://absolutewrite.com/forums/index.php) for feedback.
Find an Agent: Go to AgentQuery.com or QueryTracker.com. Search by genre, then rate them into three groups. Big fish, medium fish, and agents not on the top of your list (small agency). Look at their sales records, their clients, and their agencies. Follow them on Twitter. Look them up on Publisher’s Marketplace. Double check them at Preditors and Editors (pred-ed.com). Then read this guide to bad agents from SFWA (http://www.sfwa.org/other-resources/for-authors/writer-beware/agents/). The key here is to be educated and follow your gut. A bad agent is 1000 times worse than no agent.
Follow the Rules: Each agent will have their own submissions guidelines, so be sure to follow them when querying. They are bombarded with emails, so messing up their system could make or break your budding relationship. Most want a specific subject line in the email that will allow them to sort your query correctly. Following the rules is your first test. Make a spreadsheet with these columns: rating – name – agency – agency website - email – Twitter – details – sub guidelines – date sent – response – response date – why you contacted them – how you found them -- etc.
Wait: Don't send out all your pearls in one swoop. Send out a few and wait. If you get all bad responses, tweak your query letter, or maybe not, just see what the main "theme" is for your rejection and fix it (if you can). Send out a few more. Try not to take it too hard when you're rejected because you will be, just keep learning and moving forward. Keep track on your sheet. Try not to let it all make you crazy during this waiting time. Use the waiting wisely and work on your next book.