I LOVE LOVE LOVE NoScript. It is by far my favorite and most useful. It will block literally EVERYTHING you don’t allow it (flash). Some people might find it annoying to manually allow the sites they visit (click, click, done), but once you allow it will always be allowed unless you decide to change it. It can be accessed from the lower right corner of the browser, very easily. It will make your browsing faster as the dozens of ad, tracking, data-collection syndications never get downloaded by you. You wouldn’t believe the number of erroneous sites that are involved in a single web page. Don’t want to be tracked by facebook? disallow! This isn’t an issue for me since I use a mac, but if you have a PC, your risk of getting viruses will be GREATLY reduced.
That being said, sometimes you will have to “temporarily allow all this page” to view something correctly. It is indispensable to me.