SuperF4

SuperF4 is a very lightweight Windows utility that can instantly kill a user-defined process.
As compared to all the other similar products on the market, SuperF4 runs in the background and places an icon in the System Tray, allowing users to kill apps via predefined hotkeys.
Sadly, there are no configuration options, so you're not allowed to change this keyboard shortcut, but it's still a very fast way to kill a specific process.
The whole idea is pretty simple: whenever you want to shut down an application, especially if it's not responding anymore, just press Ctrl+Alt+F4 and you're done. The process is killed instantly and you don't have to do anything else.
The System Tray icon also gives you the option to disable the application, which is pretty helpful if you're using the some hotkey for another program too, and to run SuperF4 together with Windows.
It does make an excellent job killing processes, but there's an important thing that needs to be mentioned here: whenever you're killing an application, the unsaved work is lost, so make sure you save whatever you're doing before pressing the aforementioned hotkey.
SuperF4 works on all Windows versions and it doesn't ask for administrator privileges on Windows 7 workstations. It runs on very low resources, so it can be used on older machines too.
To sum up, SuperF4 is a very small utility that can lend you a hand whenever you're struggling to completely kill an application. You don't need to be a computer guru to understand its goal, so average knowledge should be enough to figure out the purpose of each option.