[Guyag]

Depends what you want to get out of them. I find some are mostly focused around some of the more unique/cool challenges they come across (Google[1][2], Slack[3]), and others are more about how they solve the engineering challenges they face through software and/or about their dev process (Uber[4], Twitter[5]). Some are mix of the two (Dropbox[6], Netflix[7]).

[1] https://developers.googleblog.com/

[2] http://research.googleblog.com/

[3] https://slack.engineering

[4] https://eng.uber.com/

[5] https://blog.twitter.com/engineering

[6] https://tech.dropbox.com

[7] http://techblog.netflix.com/

[CodyReichert]

Another one for Google that's really interesting is their testing blog: https://testing.googleblog.com/