Not a blog, but one of the top journals for machine learning is all open access and freely available:

http://jmlr.org

Also, see the Machine Learning section of CORR on arXiv:

http://arxiv.org/list/cs.LG/recent

A good aggregator for ML content is:

http://machinelearning.reddit.com

You may also find some good stuff at

http://www.kdnuggets.com

http://flowingdata.com/

Also, see: http://www.datatau.com/ "Hacker News for Data Science"

There's also a good stackexchange site that includes ML:

http://stats.stackexchange.com/

And there was a good site here, but it appears to be down at the moment, not sure if it's temporarily so, or permanently:

http://www.metaoptimize.com/qa