Or "search engine optimizing", "professional seo", "seo services", "seo company", "seo UK", "seo India" etc. Obviously there are more than 10 good SEO companies in the world, so perhaps you could look at TOP 10 + smaller companies within TOP 30. You could prefer companies who do not use spammy techniques (excessive footer links, unnatural keyword repetitions, meaningless texts written just for "seo" purpose) at their homepages. Stay away from sounding promises, top placement guarantees, "search engine submission services" etc. Do not believe any "testimonials" at their homepages... Usually best SEO work ranks well but you couldn`t recognize any specific "optimization" done at this site.