Exclude categories from list using widget

I need a simple widget/plugin that allows me to exclude categories from a category list on my sidebar. Just like the pages widget. I have tried several widgets but they seem not to work. I have also tried some programming with the result of reinstalling wp.

I am new to wordpress and know little programming. Hope someone can recommend me a working widget allowing me to include/exclude categories (or a problem free and safe way to get around it).