Internet Web Marketing Consultants

As the owner of an online business development company, I am always keeping my eye out for new ways to drive traffic to my web site. But how do you weed out the gimmics and those that promise great results? Also, has anyone found that banner ads and ads on search engines to provide and significant return on investment? I am very leary to try any of these services because they do not offer any sort of guarantees and I cannot afford to waste my money of phony advertising schemes. I know that there have to be legit internet web marketing consultants out there. I just don’t know how to find out who they are.