I'd say to either hire a consultant (consulting firm) or possibly look at Brainbench.com for certification & placement examinations. (Any testing is to be done on-site, in an allotted time-frame...) There may even be a service (such as Kelly services that would administer the testing, etc, for you). I'm in agreement with jvillain about the certifications, though. Just because someone is certified doesn't mean they're any good.
Look at the guys with an experience-based resume, not a certification/education-based resume. Some certs are good, but most good techs & programmers did something other than take a lame course, etc, in Visual Basic or "Web" programming. The best coders learned it because they had to.
I'd, personally, rather hire someone with no college/technical training that's been doing the work for the past 5-10 years, because he/she did it the hard way. That person learned it better, more thoroughly, and more completely. The benefit is they are more than likely still able to learn and work harder for you and your mission statement (I've seen this in quite a few cases).
Regardless, good luck!