Good question! Is this for you, or for you to evaaluate a traiiner?
First off, Muscle and Fitness Institute. $39.95 for a certification? I don't think so! Lets forget that one! I have heard mixed reviews of IFPA.
Nowadays, different certifications carry different prestige. Although some may carry more weight, so to speak [img]smile.gif[/img] than others, it all depends on what your interests are.
The absolute minimum acceptable standard for an entry level instructor would be AFAA. They provide a 3 day workshop, along with a prep course.
Next up is ACE.
Once you get beyond these 2 certs, you will find that the focus will vary. IMHO, for ski specific training, NASM http://www.nasm.org
is the ultimate certification. With its emphasis on the kinetic chain, functional and integrated training, you come away with a clear understanding of how to integrate strength and balance.
For a more traditional approach to strength training, NSCA, National Strength and Conditiioning Association are the champions.
The absolute gold standard for fitness certification is the American College of Sports Medicine, ACSM. The problem is, its extremely technical. There is a major emphasis on conducting submaximal stress tests. If you are not interested in doing that, its a good deal of time and money to invest.
Hope this helps!