Roundcube webmail is a very promising Open Source webmail client. With CPanel 11 installing RoundCube is quite easy and with no file editing of CPanel files. To install roundcube you should follow this  procedure:

1. Download RoundCube Webmail from http://roundcube.net/ .
2. Unzip it somewhere and open with an editor the
   
3. asd
4. Login to WHM of your server and open PhpMyAdmin.
5. On the first page click on Privileges Option and the choose "Add New User".
   
6. Type as the "Username" roundcube, as the "Host" localhost and as "Password" a password of your choice!
7. Check the option "Create database with same name and grant all privileges" underneath and click on the button "Go"
8. Now that you have created the database and the user for mysql click on the tab "Databases" and open the newly created database.
9. Choose the tab "Import" and upload from the folder SQL of RoundCube the file mysql.initial.sql or mysql5.initial.sql (in case you have Mysql 5).
10. Now open the file "db.inc.php.dist" in the folder config of RoundCube.
    
11. Find the line
    $rcmail_config['db_dsnw'] = 'mysql://roundcube:pass@localhost/roundcubemail';
    and alter it with the correct data you have chosen on step 6.
12. Save the file as "db.inc.php".
13. Open the file "main.inc.php.dist".
14. Find the line
    $rcmail_config['default_host'] = '';
    and with the brackets type "localhost".
15. Save the file as "main.inc.php".
16. Upload all the files (maybe with WinSCP) to your server in the folder "/usr/local/cpanel/base/3rdparty/roundcube". As the folder roundcube does not exist you should create it first and then upload the files.
17. Change the permissions of the folders "logs" and "temp" to rwx for all (777).
18. Login to http://servername/webmail and enjoy RoundCube webmail