Not a week goes by where I don’t assess our SEO status. And many weeks, during periods of significant content change, I’ll assess on a daily and sometimes even hourly basis.

Here are the web-based tools I use.

1. Shoemoney’s Search Engine Ranking Placement (SERP) Tool. This scripts simultaneously queries all search engines’ APIs and returns how your site ranks for any term. It’s a huge time save time if you tracks lots of keywords or sites on a regular basis. (Note: API results differ from browser queries and browser query results vary on a country by country basis.)
2. Webconfs SEO Tools. Webconfs, like many other SEO sites, offers a number of tools to reduce guesswork. Ones I commonly use are:
     »Keyword Density Checker to see how visible our most important keywords are or aren’t. Then I test competitor sites to see their densities. Very illuminating.
     »Spidered-Text Simulator shows the text and links that they think search engine spider see when it parses a page. Compare your pages to your competitors above and below you.
3. Compete.com’s Search Analytics. This is a new Compete service. I’m still determining its value to us. It provides detailed competitor data, and thus it could be very valuable if you use it and they don’t. They are able to show for any given keyword or phrase, all the top sites that rank for it, who does the best in terms of appearing in result sets, who does the best in terms of clickthrough, and how many matches a site gets for that term in a month. (You know Compete.com, right? They aggregate and parse request logs of major ISPs. They then know, on an anonymous basis, exactly what is being queried, what is being clicked, visit lengths and other standard web log info. It’s the data Alexa wishes they had and ComScore will no longer be able to charge a lot of money for.
4. Google Webmaster Tools. You use them right? If not, get on it. Google shows an awful lot about how they are indexing your site. Which pages are indexed, which aren’t. What’s returning 404s, what robots.txt files are blocking. It will also let you control your site links if you are big enough to have them displayed.

I’ll also save you some time. Making small changes such as a 5% tweak will not change your business model. So time well spent is only time that creates 25% change or more. Significant change is all that matters… everything else is, well, insignificant.