Coming from an agency, there are often times when there is need to perform a competitive analysis for a client in order to better understand the client's position in the competitive landscape. The main purpose of a competitive analysis should be to gain awareness of the competitive factors analyzed and to leverage the client's strengths, weaknesses, opportunities and threats (SWOT) to their advantage. So what kind of factors should be included in an online competitive analysis? Below are a few that I feel should always make the competitive analysis list:

Domain Age: The age of your domain can have an affect in the way search engine determine authoritativeness for your site. Theoretically, the longer the domain has been active, the more value it receives from search engines. Webconfs has a great tool for calculating the age of your domain and your competitors' http://www.webconfs.com/domain-age.php.

Search Engine Visibility: Take your vertical's main keyword basket and analyze how visible your site is compared to its competitors in Google, Yahoo, MSN, ASK and AOL. Comparing the number of top X rankings can give you a sense of your keyword market share.

Site Traffic: This one is difficult to compare unless you have access to your competitors' analytics, however Compete.com's search analytics does a fairly decent job of providing some insight.

In Bound Link Quality: Using a combination of Yahoo Site Explorer and a batch PageRank checker you can begin to determine the quality of back-links for a given domain. The quality of links is more important than the quantity.

In Bound Link Anchor Text: The quality of links is partially based on the theme of the linking site as well as the anchor text that is linking to you. Image or branded links aren't as high quality as keyword rich links. http://www.webconfs.com/anchor-text-analysis.php

Meta Tags: This maybe considered simplistic and old school but meta description and title tags are still important in SEO. Analyzing description and title tags can help you determine which competing sites best differentiate themselves as well as the messaging the site is providing visitors.

Paid Search Campaigns: On the other side of the fence their is sponsored campaigns and a tool like SpyFu can give you some insight on PPC competitors and keyword costs.

Blogs: Got a blog? Check out Blog Juice from Text Link Ads, which looks at Bloglines, Alexa and Technorati to compute a "juice" score.

Obviously there are other online factors to consider and I would to hear about what other people think.