Here are some guidelines for designing and choosing a logo:
- The logo should be abstract (a "blank slate") and bear little or no resemblance to the product or product name.
- The attributes (e.g. colors) of the logo should be consistent with the rest of your branding effort.
- The logo should be such that it is possible to size it to fit on your marketing material, company documents, and product.
- The logo should be unique and identifiable to someone who has seen it multiple times.
- The logo should be easy to reproduce electronically (e.g. on a web page) and in print.
Given these guidelines, it makes little sense to pay a branding/advertising firm exhorbitant amounts of money to produce the logo. You just need someone creative who knows how to use simple drawing software on a computer.