The Proxomitron is the single best piece of software to grace the internet.
Almost every major website I visit contains some sort of annoying "feature" enabled by modern browsers - the kind of feature that you wish you could disable:
Proxomitron is a local filtering proxy - you route all of your web traffic through it, and it modifies the HTML code in the pages with your desired changes. So it works with any browser, and works much more effectively than other popup-stopping programs that just auto-close the windows when they see them.
It can remove all of the above "features," plus more, from web pages before they get to your browser. Every filter can be toggled with a simple checkbox.
It has the best installation method I've ever seen: To install it, unzip it to a directory. To uninstall it, delete the directory.
While running, Proxomitron sits in the system tray. By right-clicking its icon, you can set various options including the "Bypass" option, which disables all filtering and simply passes pages through in their unmodified form. This is helpful if your selected filters are "breaking" a page that you're trying to use, or you want to ensure that nothing is modified in a secure transaction (such as online buying).
The only fault of this program is the save/default arrangement. If you make changes, you have to specifically Save them with the menu - if you don't, they won't be there after you restart the computer. The options should save automatically as soon as you change them, or the program should prompt you to save them if there have been unsaved changes before exiting. It would also be nice to have some sort of auto-configuration of IE's proxy to point to Proxomitron when it's running, and switch back to standard when it's not. These features, if added, would make Proxomitron a much more idiot-friendly program. As it stands now, it's extremely popular among geeks, but I don't think I'd recommend it to someone who didn't know how to configure IE's proxy settings.
The website is here, but unfortunately, the author recently decided to take it down and discontinue Proxomitron development. Many fan sites are still running, and have developed their own custom filters for the program, allowing it to add (and remove) all sorts of wonderful things from web pages. The best and most widely recognized is probably JD5000.
The Proxomitron has returned control of the internet back to the users. For that, I am eternally grateful, and I hope the author reconsiders his recent shutdown of the project and website.