I've used Beautiful Soup a lot with Python. It is much better than regular expression checking, because it works like using the DOM, even if the HTML is poorly formatted. You can quickly find HTML tags and text with simpler syntax than regular expressions. Once you find an element, you can iterate over it and its children, which is more useful for understanding the contents in code than it is with regular expressions. I wish Beautiful Soup existed years ago when I had to do a lot of screenscraping -- it would have saved me a lot of time and headache since HTML structure was so poor before people started validating it.
