Compatibility and Standards Compliance

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/

Acid Tests
A series of tests from the Web Standards Project to assess the standards support of web browsers. Also includes tests themselves, reference renderings, descriptions of the functions tested.
http://www.acidtests.org/

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

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

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/

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

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/

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

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

Opera Files Antitrust Complaint with the EU
Press release coving Opera Software's complaint that asks the EU to help give consumers a genuine choice of standards—compliant Web browsers. <small>(December 13, 2007)</small>
http://www.opera.com/pressreleases/en/2007/12/13/