SEO Companies?

I've attempted internet marketing with some niche internet marketing companies in the past but saw limited results as far as raising my Google ranking. A friend who is in the dental field mentioned he started working with an internet marketing company ( nextupnetwork.com ) out of Indianapolis and is pretty happy with the results. I was wondering if anyone has worked with this company or could tell me about their experience with using an SEO company. Any tips or advice are welcome!