This is a great new Open Source project that is helping browser compatibility for web interfaces. It's free for all, though a pay service is also available for priority on your "browsershots". I've been using them for about 3 weeks now and it has come in really handy.
What is Browsershots?
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 website in their browser. Then they will make screenshots and upload them to the central server here.
Sometimes the service gets busy. I am sure it's becoming more popular by the day. You may consider their pay service for faster processing. I've been giving that some thought too.

They have a queue for you to see your Browsershots as they are being processed. With the free service, you may need to extend your queue. Just click the extend button, if your queue is done before the Browsershots are ready for all of your selected OS & browser types.