Michael Adams (mdawaffe)

Just One Category will cause WordPress to display on a category archive page 
only those posts which are direct members of that category, i.e. this plugin 
will exclude from that category page all posts which belong to any of that 
category’s subcategories but do not belong to the category itself.

Just One Category

On a category's archive page, displays only the posts directly in that category, not in any sub-categories.

JohnnyPea

It adds extra option fields to the user profile page where user can select the categories he wants to exclude from the site. You can allow excluding from the “Home page”, “Archive pages (excluding category archives)” or “Feeds” and also you can set which categories can users select for excluding. You will find all these setting on “My Category Excluder Settings” page in your admin panel.
It is really easy to use. User just selects the categories he wants to exclude on the “Your Profile” page in “Exclude these categories from the site” section and hits the “Update Profile” button.
I am open to suggestions to improve the plugin !

My Category Excluder

This plugin allows your registered users to exclude some categories from the queries on your site.

Just One Category vs My Category Excluder