If you are a professional organic seo company then pls send me link and description of your website I will place your add here but pls be sure your link would be non clickable or will have nofollow attribute: .

1. SEOmoz: SEOmoz is a hub for the search marketing industry, providing an SEO Services Marketplace, a popular SEO Blog, SEO Tools and premium content

URL: www.seomoz.org

2. Bruce Clay, Inc.: Award winning internet marketing tutorials and services: Search Engine Optimization, PPC, analytics, design and SMO brand marketing site
 

URL: www.bruceclay.com

3. Just Search : Just Search are natural search engine optimization (SEO), Pay Per Click Management (PPC) & internet marketing specialists to companies

URL: www.justsearching.co.uk

4. SEO.com: Increase your bottom line with SEO.com: a search engine optimization and internet marketing company specializing in SEO and SEM services.
URL: www.seo.com