I've been using Slickdeals.net to discover good deals on things for several years now. Today I thought it'd be really helpful to be able to hide deals from companies that I don't ever buy things from (like Tigerdirect and eBay). A quick Google search turned up nothing, but playing around with Slickdeals revealed just such an option.
Open the Frontpage preferences by clicking the little gear icon at the top-right:
Any category or company set to "dislike" is hidden. Any category/company set to "like" will result in more deals matching that category/company being shown to you.
This makes Slickdeals even more useful since I can stop seeing stuff from companies and categories I don't care about and instead see more stuff I might actually be interested in.