As far as I'm aware there's no "small business server" distribution. However, you can easily install Ubuntu 12.04 LTS Server edition (the "LTS" stands for "Long Term Support" - this is generally what you want when you're running servers. You can then install/configure your LAMP stack individually (the Ubuntu installer even provides a group-install open I believe).
For control panels, take a look at Webmin (free) or Plesk or Cpanel (both commercial, paid software). Apache and MySQL can be installed using your chosen distribution's package manager.
For mail-server software, you can use a combination of Postfix (SMTP) and Dovecot (POP3/IMAP) with SpamAssassin and ClamAV for spam filtering and virus-scanning respectively.