1) W3C HTML Validation: http://validator.w3.org/. W3C HTML Validation service will check your HTML documents for conformance to W3C HTML standards.
2) HTML Tidy: http://infohound.net/tidy/ . HTML Tidy is a tool for checking and cleaning up HTML source files. It is especially useful for finding and correcting errors in deeply nested HTML and validates your HTML documents off-line on your own PC.
3) Broken links: http://www.htmlhelp.com/tools/valet/. Link Valet is a WWW Link checker. It uses an HTML table to present the links in a page, and highlights information that is likely to be of interest to you.
4) Spellchecker: http://www.spellcheck.net/. At Spellcheck.net you can enter one word or the body text to spell check: (Up to 20,000 characters). Make sure you check all of your pages for misspelled words.
5) CSS Validation: http://jigsaw.w3.org/css-validator/ . This W3C Cascading Style Sheets (CSS) validation service checks and (X)HTML documents with style sheets. Simply enter the URI of a document (HTML with CSS or CSS only) you would like validate.
Note: If you want to validate your CSS style sheet embedded in an (X)HTML document, you should first check that the (X)HTML you use is valid.
6) Accessibility Evaluation: http://wave.webaim.org//. WAVE is a free web accessibility evaluation tool. It is used to aid humans in the web accessibility evaluation process. Rather than providing a complex technical report, WAVE shows the original web page with embedded icons and indicators that reveal the accessibility information within your page.
7) Download Time Evaluation: http://www.websiteoptimization.com/services/analyze/ : To determine your download times using modem speeds of 14.4k, 28.8k, 56k, ISDN 128K and T1 Link 1.44 Mbps. Ideally, try to keep your download time for your home page size under 20 seconds (sites that take more than 20 seconds to load lose up to 50% of their visitors). For your other pages, keep them under 12 seconds using a 28.8 modem.
8) Testing using Different Browsers: http://browsershots.org/. Testing should also include using different browsers to view your Web pages. Browsershots. This is a free online platform where you can test your Web design using different browsers. When you submit your Web address, it will be added to the job queue. A number of distributed computers will automatically open your Website in their browsers. Then they will make screenshots of the O/S and browser views you request and upload them to their central server. It can take about 30 minutes.