It will be a nightmare for you if your google account gets hacked,Most of the people in these cases waste their money contacting the password recovery services wasting their money,I dont say they dont get back password,But you can do it by putting in some efforts
I will begin with Google. it's a pity thing your account got hacked. in most cases it was you own fault that it got hacked. in rare cases i it the hacked who really did something . you should take care. Read more on how to prevent your self from getting hacked.
Now coming back to the main discussion . you can do the following to once hacked.
Change password:- The first thing you need to do in case your account is hackedis change your password and all security details. in most cases the hacker doesn't has your password but cookies.So once you change it the problem is solved. In case you are not even able to log in use the following link to reset your password
Contact Google:- Once you have performed step one. immediately contact Google.You can use one of the forms based on your account type.You will be asked the exact creation date of your Google Account and also a copy of that original ?Google Email Verification? message. if you are lucky then only google will help you . In any case you will receive a reply from form them.
With Gmail id:- If you use a gmail id to login then use this form to contact google.
Without Gmail id:- If your Google Accounts is not linked to Gmail i.e you dont use gmail id to login then use this form.
Inform all your buddies:- Send a mail to all your buddies informing them that your account has been hacked.Who know what the hacker might have done.