Squeeler is a Mac OS X app that sits quietly in your menu bar and alerts you when it sees something hogging CPU, possibly slowing down your computer and definitely draining your battery if you're not plugged in.
Click the download button above to download the zipped application. Just unzip it and drop it into your Applications folder. Running it will put a little icon in your menu bar, and then it will start watching your processes. You can click on the icon and select Preferences to adjust the sensitivity, but otherwise, that's all you need to do.
When it detects a runaway process, it will display a notification. Clicking that notification will bring up the OS X Activity Monitor, letting you decide if you want to kill it or not.
Squeeler is free and open-source (MIT license). If you find a bug, or just have a suggestion, feel free to create an issue on GitHub...or even better, fork it and hack on it yourself, and send me a pull request.