I wanted to add another library of classes to a Zend Framework project and autoload them, I created a folder called application/vendors/ to hold vendor libraries in seperate folders of their own. For example, using some CURL classes from Sem Labs, these classes would live in the application/vendors/semlabs/ folder.

I renamed the classes to match the Zend Framework class naming structure for autoloading:

class Vendors_Semlabs_CurlRequest extends Vendors_Semlabs_Curl
class Vendors_Semlabs_Curl

In a model I wanted to simply create that class and have it autoloaded automagically without having to require the class file or anything like that:

$curlRequest = new Vendors_Semlabs_CurlRequest();

Getting this to work as intended was a bit of mission, ended up with the code for autoloading vendor classes in bootstrap in the _initAutoload() method:

<?php
class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    /**
     * Get the autoloader the base path for the module (application), 
     * add a new resource autoloader for the vendors folder to include vendor classes 
     * 
     * @return void
     */
    protected function _initAutoload() 
    {
        $autoloader = Zend_Loader_Autoloader::getInstance();
 
        $r    = new ReflectionClass($this);
        $path = $r->getFileName();
 
        $vendorsAutoloader = new Zend_Loader_Autoloader_Resource(array(
            'namespace' => 'Vendors',
            'basePath' => dirname($path).'/vendors',
        ));
        $vendorsAutoloader->addResourceType('semlabs', 'Semlabs/', 'Semlabs');
        $autoloader->pushAutoloader($vendorsAutoloader);
    }
 
}