Though I prefer GMail web interface, still many people use desktop mail client for other advantages such as multiple account handling. To do this you need to sync your contacts in GMail with Desktop mail client. This simple HOW-TO talks about getting it done this with Thunderbird Add-on called Zindus. Here I am using Thunderbird 3.1 and Zindus 0.8.13.3.
Step-1: Thunderbird -> Tools -> Add-ons -> Get Add-ons -> Search for “Zindus” -> Select the Zindus add-on and install it. Restart the Thunderbird.
Step-2: Thunderbird -> Tools -> Zindus -> Settings -> Add -> Sync with “Google” -> Enter your GMail address and Password -> Test Connection -> OK
Step-3: Back to Settings dialog -> Sync Now. This should sync all your contact in “Personal Address Book” of Thunderbird with GMail contacts.
Step-4: Thunderbird -> Tools -> Address Book -> Personal Address Book. You should see your GMail contacts listed here