One of the first things any net-savvy person will tell you is that SEO, or search engine optimization, is the most important thing you can do for your website whether your business is internet-based or not.
The value of these tools is that they give you the ability to enhance your site's performance in the search engines by making it more visible.
5. Broken Link checker
You go on a website, you click on a link, and behold, it leads nowhere. There are quite a few sites offering link checking services, but the best I've found is brokenlinkcheck.com, which actually discovers broken links and tells you where to find them. The other link checkers I've found either only check one page at a time, obliging you to load each page of your website, or won't check pages in subdirectories, which is no good at all. Having broken links is a big SEO no-no because when someone stumbles across a link to your site and it leads nowhere, it makes you (and your site) look unprofessional.
4. Backlink checker
There are loads of these, and each of them promises to give you the best results. As a matter of fact, a simple check of the url of your website in a search engine will provide links to your website from wherever it is linked. None of the checkers I used showed all the sites that link to my site. backlink.com, for example, declares I have none. urivalet.com gave me 17. iwebtool.com gave me 45. ongsono.com gave me none with Google, 57 with yahoo and over 1,000 pages indexed. Those must be duplicates or something. bluebacklinks.com gives me 53. Google Webmaster tools gives me 116 at the most, but the search engine gives me 169 (689 at the most with omitted results).
3. Webmaster Tools
The best reason to get a Google account. There are many excellent features on it, including the ability to remove URL's from the search engine index -- whether they belong to you or not. They allow you to submit sitemaps and alter your robots.txt files. It's all connected to AdWords, AdSense, Analytics, and Apps, each of which are very useful. Personally, I don't use AdWords and AdSense, but I use Webmaster Tools, Analytics and Apps all the time.
2. Sitemap Generator
The best sitemap generator I know is xml-sitemaps.com. Sitemaps are an invaluable tool for ensuring that your site ranks well in the search engine results. It also shows you what content is or isn't being displayed online. If you delete any pages or change the URL, be sure to create a new sitemap or you may have problems with broken links.
Update: brokenlinkcheck.com have responded to my thankful feedback and told me they do indeed have another tool: a sitemap generator that offers a larger limit than the 500 pages checked by xml-sitemaps. See it at web-site-map.com.
The W3C Markup Validation Service was created by the World Wide Web Consortium to develop web standards and encourage consistency in coding and browser support. Using this tool allows you to check your site's source code for errors and correct them. It will even give you the solutions to your code problems and write you an alternative style sheet which you can then download. A standards-compliant website will load quickly in a browser and show up well in search engine results. Websites that don't validate correctly may load more slowly or get lower rankings.
Each of these tools is invaluable in helping me to make sure my site is the best it can be and has the best chance of performing well in search results. If you know of any tools you think I might find useful, let me know. I'd love to hear from you.