Blog Content Writing Services (High Quality)?

I'm probably biased.

What you paid is what you get. More money you spend, you should get better quality content.

You can search writers at freelancing sites. And also check their reputations. e.g: guru.com, odesk.com.

Why not look into the "Warriors for Hire" thread, there are several great writers offering services here, and many of them understand marketing, SEO, and crafting articles and blog posts to suite your audience.

If not iWriter.com is another option.

If you want high quality, try Constant Content.

Try:
onlinejobs.ph (John Jonas of replacemyself.com)
writeraccess.com
textbroker.com
iwriter.com (Brad Callen)
ccarticles.com (Winson Yeung)
constantcontent.com
99centarticles.com
myarticleexpress.com (Unique Article Wizard)
godotmedia.com
articlez.com
hirewriters.com
contentproz.net
watermyblog.com
scripted.com
wlmarketing.com
fiverr.com
odesk.com
elance.com
freelancer.com
copypress.com
The Warriors in this thread, or The Warriors for Hire section.
There are 1,000s of services out there!

p.s.
Check my signature link.

I use www.greenlightarticles.com/

I'm biased too... I'd also like to say some of those content mills mentioned make me very angry. Rather than give them money just take it out your pocket and set light to it. In the long run the result will be the same.

Don't throw quantity at the problem. Work with one writer, get a consistent tone of voice and find the subjects that get shared and read by potential customers. Remember it's not just whether your content was the right price, it also has to entertain or inform the end user. Preferably both...

Content mills are generally junk. The writers have to crank out more words than anybody would ever recommend if they want to eat that day. You would need 1000 monkeys banging on 1000 typewriters to earn the minimum wage, that should tell you all you need to know about the quality.

I know one guy that does really good work. His name is Michael Chibuzor (contentmarketingup.com). He also does guest posts,ghost writing,and book writing.

Quick tip when hiring a writer:

Make sure you are clear regarding your project parameters. Always include a link to a sample article. If ordering KEYWORD articles, make sure you indicate your repetition threshold percentage.