Greasemonkey script shows the Google Calendar agenda on the left-hand side in Gmail (screenshot). That was a quick hack, considering Google Calendar is just some hours old. Note that running Greasemonkey scripts on top of Gmail may be against the Google ToS and cause problems with your account.
Deepak Gupta is a IT & Web Consultant. He is the founder and CEO of diTii.com & DIT Technologies, where he's engaged in providing Technology Consultancy, Design and Development of Desktop, Web and Mobile applications using various tools and softwares. Sign-up for the Email for daily updates. Google+ Profile.