Due to cross-browser compatibility issues, web designers need to test their pages on various browsers and operating system platforms. Here are a few services that will take an URL and display how that page looks in various browsers and operating systems.

• BrowserCam.com - well known for it large range of browser and operating systems including PDAs. Remote access and virtual machines that you configure yourself are available.
• CrossBrowserTesting.com - free 5 minute sessions available. Ability to test your AJAX and Javscript.
• BrowsrCamp.com - Mac testing with remote access
• BrowserShots.org - Free open-source. Let's you select screen resolution and whether to disable Javascript or Flash
• BrowserLab.Adobe.com - requires and Abode login to use (but is free). Has slick user interface with zoom and ruler
• NetRenderer - Free and fast screen renderer for IE browsers
• TotalValidator.com - Free. Ability to delay taking screen capture picture. Includes HTML validator, accessibility validator, spelling validator, and broken links validator.
• IECapture.com - shows you what your site looks like in the latest IE version (include beta's)
• iCapture - Screen capture using Safari on Mac
• LitmusApp.com - Test websites and HTML newsletters as well.