How to find out how many times a term gets searched

I want to see which is the more popular search

[DJFlite]

I run a site which is a buyers guide for certain products. I am in the process of SEO right now and I have a question.

Many of the products I review have names that are combonations of words letter and dashes. For example, the M44-7 or the 505 SK-II. My problem is that some users will enter these product names in different ways. So my question is how can I find out which way of writing the product is the most popular search.

For example,

the m44-7 can also be written as M447 or M-447

How can I find out which or these combonations is the most search on a specific search engine. I know there are sites like this but I dont know them.

Any help is much appreciated.

[operafan]

Have you tried inventory.overture.com suggestion tool?
or google's search which is more precise
[adwords.google.com...]