We all have seen our share of articles on how to make your site friendly to search engines, but this article is probably one of the best I've seen online. The article is written by Ross Dunn and is titled, "Is Your Website Search Engine Friendly? Your Personal Checklist":
The following is checklist designed to help you gauge the search engine friendliness of your website and, if you are in the midst of planning a website this checklist will help you avoid the common pitfalls of unfriendly designs. Complete Story
The article is a must read for those hoping to improve their rankings on search engines such as Google and Yahoo.