Now that you have your site designed and coded, it is time to do some quality assurance or QA.
Validate your CSS here.
Validate your HTML here.
A thorough checklist of best practices.
Use BrowserShots to see how your site will appear on several different browsers. Although this is only an approximation, it is a great service.
Use GoogleTrends to see how popular your keywords are.
Use this service to see what search engines see when they scan your site.
The Web Page Analyzer tests your site to see how fast it loads.
Check your links using this service from the W3C.
If you are concerned about how accessible your site is, use the Cynthia Says portal.