www.core77.com - focuses on industrial design. There is a blog, but also a portfolio and jobsite for designers (www.coroflot.com)
www.designobserver.com - is also great. The writers are some of the top practitioner in the world. It is a little NYC biased, and a touch snobby, but a great resource.
www.thedieline.com - is a blog focused entirely on packaging design. Frequently updated with great design examples. One nice thing about this blog is that they feature high end stuff in boutiques and clever designs you could find at a super market.
Far too many to list, much less read. Find one that you think is good, and subscribe to the ones they link to.
Avoid ones that: never criticize; very frequently post lists, free brushes/templates/vectors/tutorials; use the word "inspiration"; never post anything whose design-relatedness is indirect or not immediately clear or without commentary; or are authored by recent graduates.
