PHPMoney is a unit-tested Money pattern implementation (sans currency -- which is on the TODO list) for PHP 5.3+
Add the following item to your composer.json's require section: "lusitanian/phpmoney": "dev-master"
The classes are set up in a PSR-0 compliant manner and will work with any PSR-0 autoloader if you don't install the package with composer (which generates an autoloader automatically).
The library includes a MoneyFactory that will create Money instances for you using the best-available MathProvider that will work on your installation of PHP.
Example Usage
<?php
$factory = new PHPMoney\MoneyFactory();
$twoDollars = $factory->createMoney(200);
$threeDollars = $factory->createMoney(300);
$fiveDollars = $twoDollars->add($threeDollars);
echo $fiveDollars->format();
You can, of course, also create Money instances without the factory. You will need to pass each Money instance an instance of a MathProvider (you can and should use the same MathProvider instance for multiple Money objects).
<?php
$bcMathProvider = new PHPMoney\MathProvider\BCMathProvider();
$oneDollar = new PHPMoney\Money(100, $bcMathProvider);
$twoDollars = new PHPMoney\Money(200, $bcMathProvider);
The tests are in the tests folder and reach 100% code-coverage. You need phpunit to run them. A phpunit.xml file is included.