Here’s a list of Official Google accounts on Twitter:
twitter.com/Google – our central account
twitter.com/Blogger – for Blogger fans
twitter.com/GoogleCalendar – user tips & updates
twitter.com/GoogleImages – news, tips, tricks on our visual image search
twitter.com/GoogleNews – latest headlines via Google News
twitter.com/GoogleReader – from our feed reader team
twitter.com/iGoogle – news & notes from Google’s personalized homepage
twitter.com/GoogleStudents – news of interest to students using Google
twitter.com/YouTube – for YouTube fans
twitter.com/YouTubeES – en Espanol
twitter.com/GoogleAtWork – solutions for IT and workplace productivity
Full list @ Google Blogs.