I am aware that I can access GMail securely using SSL however what I would like to learn or know is that once I send an email, does that email remain encrypted?
For the most-part, "no," because SMTP transactions are not encrypted by default. If both sites do support encryption, and share the same mechanisms for encrypted transport, then this is possible, but it can't be guaranteed.
To be sure that your eMails are encrypted, encrypting them client-side can provide you with the assurance you need. Some eMail programs may have encryption features built-in (such as Pegasus Mail and some others), but chances are you'll need to use a third-party encryption tool like OpenSSL, GPG, or PGP (or rely on 7-Zip's AES encryption features to encrypt your message contents, file attachments, etc.), especially if your recipient isn't using the same eMail client software that you are. A challenge you may also run into with such third-party client-side preparations is that your recipients will also need to know how to perform the decryption.
Also, there are some portions of your eMail messages that cannot be encrypted for practical reasons, such as the destination address (otherwise how will the mail servers know where to send your message?).
Many web-based eMail solutions, and also some POP3/IMAP4/SMTP servers, are accessible with encryption enabled. This is client-to-server communications, which is not the same as server-to-server communications (which is what is being asked about).
Although having client-to-server encryption is great, it's only securing one aspect of eMail transportation. The other places where your eMail could potentially be available to third-party observers in an unencrypted form are:
It is usually assumed, however, that the recipient has taken reasonable measures to protect their system from basic security threats, and so the focus is typically on encryption between the sender and the recipient. Using client-side encryption technologies can certainly eliminate administrative issues with mail servers (e.g., untrustworthy staff at the ISP who like to snoop around in other people's eMail inboxes).
For a message like "Hi honey, I'll be picking up some groceries on he way home," encryption often isn't needed at all. For a message like "The password for the VPN is TunaBreath42," encryption is clearly beneficial. Weighing the importance of encrypting your eMails is only something that you can judge.
The SSL encryption only pertains to your web session with GMail, not the email itself. This means people cant snoop and see your login and password information.
Email can be encrypred on transport, however there is no guarantee that it is available at both ends.
If you want to truly have private email, look into 3rd party encryption tools, such as GNUPGP.