Adobe BrowserLab is an amazing tool. I have used this tool so much when it comes to testing a website. It has every major browser AND lets you set up a custom list of browsers you want to test in. It even gives you the option to onion skin the displays between browser so you can easily compare what’s different in each browser. This tool is free to use as long as you have an Adobe account, which is free to create. It’s all web based, so you can use it anywhere without downloading anything. The only downside of BrowserLab is that it renders the website to an image, so you cannot test functionality. You can learn more about this great tool here.
BrowserLab only has support for IE8 and IE9, so if you need to test lower versions of IE (5, 6 and 7) this program has it all. It’s only for windows, but worth the download. It has the ability to test in ALL versions of IE (although if your computer only has IE8 on it, you can only test up to that browser version) and you can test browser functionality as well. This can come in handy if you’re dealing with z-index issues surrounding Flash or jQuery. You can download this program here.
Spoon Browser Sandbox
This website is another web based browser testing service that is free. It also has an upgrade option that lets you test on all of the legacy browsers. This service allows you to test in Chrome, Firefox, Firefox Mobile, Opera, Opera Mobile, Opera Mini, Safari and IE 10. If you like it enough and want to go PRO with it, it’s a small $12/mo subscription. You can access the Browser Sandbox here.
There are plenty more websites and programs that help with cross-browser testing. For a more in-depth list, view this one put together by Smashing Magazine.