There are hundreds of SEO companies out there who sell their SEO techniques to help improve your rankings in the search engines. They can be expensive but most of all they can be risky. If you are thinking of purchasing SEO services from anyone or any company, do your research first.
Go to SEO forums or forums like digitalpoint to see what others have to say about certain SEO services and companies. Also, using Google is pretty wise. You might find something there that you cannot find anywhere else.
Don't go with any cheap services if you do decide to purchase some SEO assistance. The bigger companies and more reputable companies may charge a lot more but they have the reputation and customers to back up their services.
One company to definitely avoid is sayseodesign.com. They have been known to scam A LOT of people. See the following thread for yourself: http://forums.digitalpoint.com/showthread.php?t=854797
Good luck on finding the right SEO company for you and your site!