Looking for a checklist, or comparison site.   
How do you evaluate SEO/SEM companies? What are common services/prices?
seo
SEO in my personal opinion, really is more of basics your web developer should be doing from the start of building your site. There are some optimizations you can do along the way if you're unable to make your URL's friendly or some of the other heavier lifting things, but why you would pay for this when you already had someone build the site is crazy to me. The service part that I think I could see being worth paying for is market research about your site. I've seen a company that went out and found out what keys words were really the best for a sites content/market and helped to tailor the content of the site more accurately towards what their market wanted. In the end it wasn't so much SEO as it was just getting their site to match what people really wanted to find on their website. If someone keeps arriving on your site with the search term How to boil hot dogs and you're site only talks about hamburgers, then there's potential. However dumping Hot Dogs all over your meta data just to increase traffic is a bit of a jerk move and the main reason I hate these so called SEO-experts.