Assuming contractors take jobs to do IT work, consultants are brought in to lead and advise, we are talking more that MSCE or A+.
The Information Systems Examination Board has an international acceptance that is growing fast. They have a consultancy exam. More details at http://www.bcs.org/iseb/
Alternatively, look for IT qualifications and experienced and membership of something like the Institute of Management Consultants who have a framework by which they judge the skills of their members. More info at:http://www.imc.co.uk/our_standards/competence_framework.php