Dois serviços para a busca de endereço via CEP.

get-address-republica-virtual.php

<?php

function republicaVirtualGetAddressByCep($cep, $format = 'json') 
{
    $ch = curl_init("http://cep.republicavirtual.com.br/web_cep.php?cep=$cep&formato=$format");
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $data = curl_exec($ch);
    curl_close ($ch);

    return $data;
}

get-address-widenet.php

<?php 

function widenetGetAddressByCep($cep, $format = 'json') 
{
    $ch = curl_init("http://apps.widenet.com.br/busca-cep/api/cep.$format?code=$cep");
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $data = curl_exec($ch);
    curl_close ($ch);

    return $data;
}