I did negotiate my first contract myself since I didn’t have representation at the time--and didn’t have enough time to really hunt when the publisher came calling.
I wouldn’t recommend doing it by yourself, but sometimes it’s just not an option—agents are hard to come by, and you can get an offer from (usually small-to-mid-sized) publishers before you’re able to land a literary agent.
There are posts, by agents, on negotiating your own contract: the "Agenting 101" series (look for it on the right hand side of the page. There are eleven references) on the Pub Rants blog by Kristen Nelson, a blog entry called "Ten Things to Know if You Go Commando" on agent Janet Reid's blog, and a series called “Contracts 101” on the BookEnds Literary Agency blog:
There’s a guest post by agent Holly Root with Waxman Literary Agency on negotiating contracts: http://tinyurl.com/ybedos7
A general post by an agent on negotiating your own contract.
Another site I found helpful showed a sample author contract, just to give you an idea what the document may look like: www.writecontent.com.
Stroppy Author blog ran posts covering each section of a contract. Just scroll down for all the posts.
Usually publishers will go off a basic template contract—what’s known in the industry as a “boilerplate.” Publishers will expect counteroffers (I countered on my contract), but likely won’t budge too much from the original offer.
If something in the contract seems a little off to you, though, the information on these different blogs can definitely help keep you from being taken advantage of.
Hope this information will help some folks out there. :) Google searches on this topic are sometimes hard to sort through.