Zend Optimizer
Or
IonCube

Installed on server
Available on many hosts

  

No server changes are needed as long as safe_mode is turned off and enable_dl is turned on.
Test Script

Not sure if your server has Zend Optimizer or will support Ioncube? Download our small test file and it will let you know right away.

Download test script (3 KB)
Upload to your web server and open test.php