As confusing as search engine optimization can be for most newcomers, selecting a SEO firm can be almost as daunting. There are many considerations and often times companies are confused about how to go about selecting the right company.

Referrals are one of the best ways to find a search engine optimization vendor since there is a learning curve for most companies that have never used one before.

It’s important to note that many top search marketing companies and consultants are in a position to pick and choose their clients so it’s best to be very specific about your goals and any requirements you have when contacting them.

Below is a list of resources to help in researching search engine optimization consultants and companies:

SEMPO - This is the leading search engine marketing industry association web site. You can submit a project request and SEMPO members will reply. There are currently 405 members world wide.

SEO Consultants - Strict inclusion guidelines for this directory of search engine optimization specialists and companies makes sure vendors do not engage in search spamming. They claim to reject 70% of the consultants that apply. There are 150 SEO consultants and firms currently included.

Marketing Sherpa’s Guide to SEO Firms, 4th Edition - Offers a very detailed look at 121 Organic SEO firms. Yes you have to pay $149 for the guide, but the information allows you to compare firms on may levels ranging from clients to pricing to tactics.

Marketing Profs Vendor Selector - This is a newer list of the top SEM and SEO firms with additional information on each. There are 48 world wide SEO firms listed.

TopSEOs.com - Ranks the top 30 SEO firms world wide each month based on competitive advantages, services and pricing levels support, unique attributes and performance.

There are other sites that list SEO companies like seopros.org and semlist.com but the criteria are not as stringent for inclusion.

Also, here is a good article from Search Engine Watch on SEO Vendor selection based on a Search Engine Strategies session.

While TopRank’s search engine optimization services are listed in every resource mentioned above, the best course of action would be to establish specific criteria and gather a list of SEO companies from a variety of sources: referrals, industry resources, forums, and even conferences and then interview each candidate firm according to the criteria you’ve established.

This can take some time, but the payoff can be a high value, appropriate cost relationship with a SEO vendor that best meets your needs in the short and long term.