I like Zend FrameworkÂ’s Zend_Filter class. ItÂ’s basically a set of methods for validating untrusted data. Although the two arguably most important features isEmail() and isUri() (the latter can be worked around with Zend_Uri) are still missing, the whole thing looks promising already.
Zend_Filter provides a library of static methods for filtering data. For input filtering, you should use Section 9.2, Â“Zend_Filter_InputÂ” instead, because it provides a framework for filtering input using the methods provided by this class.