To Delete An Account First Log Out Of All Google Services, Then Log Into That Account , Click The Gear Icon > Mail Settings --> Accounts & Import --> Other Google Account Settings --> My Products - Edit:
a) "Remove Gmail permanently": this removes the Gmail service but keeps any other Google services (Reader, Docs, Blogger ...). All your emails and contacts are deleted permanently. You need to specify a non-Gmail email address as your new login.
b) "Close account and delete all services and info associated with it": this removes the whole Google account including all services that you used with this log in (YouTube, Picasa, Blogger ...). This step is irreversible and you can never use the same username again.