CSS3 . info - CSS Selectors testsuite
- Test to determine whether your browsers supports all CSS selectors.
- http://www.css3.info/selectors-test/

IE Netrenderer
- Online tool allowing to verify how websites appear in Microsoft Internet Explorer 5.5, 6 and 7.
- http://ipinfo.info/netrenderer/

Web Browser Standards Support
- Tables comparing support for different feature of HTML, CSS, DOM, and ECMAScript in Internet Explorer, Firefox, and Opera.
- http://www.webdevout.net/browser-support

Browser Zoom Comparison
- Compares the zoom function and its results on all the major browsers.
- http://alastairc.ac/2006/11/browser-zoom-comparison/

QuirksMode DOM Compatibility Tables
- Provides detailed studies and suggested work-arounds for various browser incompatibilities relating to modern standards.
- http://www.quirksmode.org/dom/compatibility.html

Wikipedia: Comparison of Web Browsers
- Provides various tables giving an overview of the features and support for various standards present in a number of different browsers.
- http://en.wikipedia.org/wiki/Comparison_of_web_browsers

Robin's HTML 4.0 Conformance Test
- Test a browser's support for new HTML 4.0 elements. Includes a table of results for serveral popular browsers.
- http://www.robinlionheart.com/stds/html4/

Browsershots
- Generates screenshots of how websites appear at vraious resolutions in several commonly used web browsers.
- http://browsershots.org/

Acid2 Browser Test
- Test page published by the Web Standards Project to assess the standards support of web browsers. Also includes a reference rendering and description of the functions tested.
- http://www.webstandards.org/action/acid2/

Acid2 in Major Browsers
- Screenshots and discussion of the rendering of the Acid 2 test by different versions of various browsers.
- http://www.howtocreate.co.uk/acid/