* Use Google's site targeting ads stats to check what sites are running AdSense and getting a lot of traffic (you don't even need to buy ads on them to do this)

* Go to Compete.com to get the top keyword phrases competing sites rank for and create content targeting the same keywords. You can also run the keywords through Google's Traffic Estimator to sort the keywords by Google's value estimates.

* Beyond that, you can run Google's site targeted ads or general contextual AdSense placement reports to find out what pages are the most popular on competing sites, and then create content covering the same topics.

* Compete can be used to see how strong a brand is in its field. The top keyword in the credit card category is Capital One. Both www.capitalone.com and capitalone.com are also in the top 5 keywords. They are obviously a leader in that space. You can also see what percent of a website's traffic originates from its brand related keywords.

* You can search for a broad match phrase to see how established your site is inside a vertical, how consolidated a vertical is, and how much potential upside you have by increasing your share of search traffic.

* Compete can also show you the if a competing site is heavily reliant on a few strong keywords or if their traffic distribution is wider. This can be used to see sites worth investing in (especially if you understand search relevancy algorithms) or sites which have a lot of risk and are worth avoiding.