You've Got Gmail for Trillian

You've Got Gmail for Trillian is a plug-in for the popular messaging client that allows you to check for new email messages while you are chatting with your friends. The plug-in retrieves the number of messages and the header information from the unread emails.
The extension can be used to periodically check your Gmail inbox or another mail account that uses the POP3 protocol for new messages. You can add multiple accounts and configure a separate check interval in order to prioritize the accounts.
You can select a message from the list in order to view the title, the date and a short description. Unfortunately, the add-in does not allow you to read the content of the email. However it lets you access the email account by opening the account email page in the Internet browser. Here you must enter the user and the password to login.
When you are not using Trillian the extension can still notify you of new email messages by displaying desktop notifications. You can customize the way that new mails are announced by changing the popup text, size and display time or by adding an audio alert.
The behavior of the plug-in can be customized in order to suit your needs by selecting the action for clicking on the email list or the desktop alert.  Every email account can be customized individually if you want to disable the email notifications or to adjust the time interval for checking the inbox.
Overall the extension is very useful if you want to be permanently informed about the new messages from your email account.