Browser Shots
Browsershots makes screenshots of your Web design in different browsers. It is a free open-source online service created by Johann C. Rocholl. When you submit your Web address, it will be added to the job queue. A number of distributed computers will open your Web site in their browser. Then they will make screenshots and upload them to the central server here.
http://browsershots.org/

Web Security
Web site security and compliance should be a top priority for organizations intent on protecting sensitive company, customer, and employee data, on meeting regulatory and corporate compliance requirements, and on defending against the high cost of a data breach. Web sites and their applications are high-focus targets for hackers because they provide a direct route to corporate or personal data.
http://www-01.ibm.com/software/rational/offerings/websecurity/

Ping Dom
Pingdom offers cost-effective and reliable server, network and website monitoring. We use a global network of servers to monitor our customers' sites 24/7, all year long. The service includes statistics for uptime and response time, and can send out alerts via SMS and email.
http://tools.pingdom.com/fpt/

Dead Links
Put your website or weblog home page URL in the input box and a little spider will read the html code and check for the broken links. The spider splits links in two categories, internal, from the same host, and external, outgoing link to different domains. Once you have put your start URL the bot will visit your website and follow all links checking for their status. When finish you will see a report showing all the bad links found, not only 404 status.
http://www.dead-links.com/

Crawl Test
To run the crawl test tool you just need to register for a FREE SEOmoz account. Currently we are limiting basic members to one report per 24 hour period and the tool will only test 5 pages at a time. PRO Members can run as many reports as they like and the crawl test will test 50 pages at a time.
http://www.seomoz.org/crawl-test

Web Site Optimization
Try our free web site speed test to improve website performance. Enter a URL below to calculate page size, composition, and download time. The script calculates the size of individual elements and sums up each type of web page component. Based on these page characteristics the script then offers advice on how to improve page load time. The script incorporates the latest best practices from Website Optimization Secrets, web page size guidelines and trends, and web site optimization techniques into its recommendations.
http://www.websiteoptimization.com/services/analyze/

Any Browser
Check out your site in different screen sizes.
http://www.anybrowser.com/ScreenSizeTest.html

Pink Juice
There are various online services offering automated web page checks. pinkjuice.com/check is just a simple tool generating links to the report pages of some of those services, including emulators, validators, and accessibility checkers.
http://www.pinkjuice.com/check/