Here is the list for most useful official Google blogs in English with their descriptions:
The Official Google Blog – Insights from Googlers into our products, technology and the Google culture.
AdSense Blog – A look inside Google AdSense. With newbie, optimization, AdSense features, and more.
Adwords API Blog – The official source of information about the AdWords API from Google.
Adwords Blog – Google’s official blog for news, information, and tips on AdWords.
Analytics Blog – Here you can get the latest news, tips, and resources from the Google Analytics team.
Android Blog – Blog for developers working with Android, An Open Handset Alliance Project.
Base Blog – Get news, tips, and resources straight from the Google Base team.
Checkout Blog – The official Checkout Blog with news for sellers using Google Checkout.
CPG Blog – News and notes from Google’s Consumer Packaged Goods (CPG).
Custom Search Blog – The latest news, updates and tips from the Custom Search Engine team.
Data APIs – Official Google Data APIs blog.
Desktop APIs – Your official source on the Google Desktop APIs.
Docs Blog – News and notes from the Google Docs team at the official Docs Blog.
Enterprise Blog – A blog about enterprise information, search, and the users that live there.
Gadgets API Blog – Intended for people who use the Google Gadgets API to write gadgets.
Gears API Blog – Keep up to date on Google Gear’s progress with Gears API Blog.
Gmail Blog – News, tips and tricks from Google’s Gmail team and friends.
Grants Blog – We started this Blog as a place to read about the latest Google Grants news and information
Lat Long Blog – News and notes by the Google Earth and Maps team.
Mac Blog – Macs inside Google. The official Google Mac Blog.
Mobile Blog – News and views from the Google Mobile team.
News Blog – The official blog from the team at Google News.
Notebook Blog – At the Notebook Blogs you can read news and tips from the Notebook team.
Open Source Blog – Open source at Google with news about Google’s open source projects and programs.
OpenSocial API Blog – OpenSocial provides a set of APIs for social applications across multiple websites.
Orkut Blog – Your official guide to staying beautiful on Orkut.
Orkut Developer Blog – Learn about APIs, changes and events related to the Orkut developer platform.
Picasa Blog – News, tips and tricks from the Picasa team at Google.
Reader Blog – News, tips and tricks from the Google Reader Team.
Research Blog – Google research blog where Googlers write about their public research.
Security Blog – The latest news and insights from Google on security and safety on the Internet.
Talk About Blog – A blog about voice, IM and open communications with Google Talk.
Testing Blog – If it ain’t broke, you’re not trying hard enough.
Video Blog – Celebrating creative works from the many contributors to the Google Upload Program
Web Toolkit Blog – About the open source Java software development framework for AJAX applications.
YouTube Blog – Official YouTube blog for latest features and happenings.
Tell me if any one is missing.I will add it