Great aggregated list of sites to find bloggers, but I did want to point out a few things:
First, while these sites might be useful, I don't think enough was said regarding the actual time it takes to post, weed out and find that perfect blogger.
The problem with most freelance bloggers that we have found at Biquitous is that they are writing for multiple blogs/websites, and therefore, their ability to deeply understand your specific needs and company objectives is limited because of that.
They may be good writers and bloggers, but their knowledge, expertise and passion for your subject matter is something that leaves a lot to be desired.
Finally, there's the issue of cost. Sites like Elance.com and Guru are great because they are free to post, but others like the job sites and CraigsList cost money, and for smaller firms starting out, posting job openings for full time blogging on more than 1 site can be a costly endeavor depending on the overall budget of the project.
Either way, this is a comprehensive list, and a great starting point for most businesses looking for high quality bloggers and writers.