Wikipedia Lens for Unity allows you to serch Wikipedia articles directly through Unity Dash. When you click on a result it will automatically open in Firefox, Chrome, Opera or whatever browser you have set as default. For the time being you can't filter the displayed results. To install it open a terminal and type:
sudo add-apt-repository ppa:scopes-packagers/ppa
sudo apt-get update
sudo apt-get install unity-lens-wikipedia
Logout and then back in, launch Dash, select it from the lenses list and type in your search. An article snippet and a thumbnail (where applicable) will be shown.
Other useful lenses and scopes that I have written about in the past are Calculator Scope, YouTube Lens, PirateBay Scope and Grooveshark Scope.