We are a big fan of Conversion XL and the work they do. One of the early adopters of conversion rate optimisation they talk about everything related to experiments and conversion.
With a focus on growth hacking. Quick sprout covers more than conversion rate optimisation including SEO, email and other channels. Their approach to business growth definitely reflects in their ideas and as such warrant a place on this list.
Purely focused on CRO the Daily Egg has a great backlog of articles about anything from data analysis and testing to how to speed up your website. Well worth checking out once a week to keep up with their content.
Many testing software companies have their own blogs and most have great content. Convert.com is no different. Their cover all the basics and then some.
One of the most established testing tools out there Optimizely has been around for a very long time. Their blog gives a huge amount of information about testing ideas, testing plans and more. Very well worth keeping an eye on.