If you use Chrome anyway. If you haven't tried Chrome - give it a whirl, I was a diehard Firefox user until I tried out Chrome.
There is an extension that can block sites on Google Search. It is called the "Personal Blocklist
". Within seconds of installing it - the annoying sites that use whatever technique they can to get to the top of a Google Search were blocked (by me, you just click on "block " in the search result and they disappear!)
You can opt to show the blocked results at anytime - so if you wanted to see them - they are easily there, but hidden.
Very cool - very very cool. There was at least one or two sites I blocked immediately - including the annoying ones that pretend to show answers but then want you to log in to read them (sometimes with a paywall).