This is widely known, but I still run across people who use IE 7, and/or Firefox but don't use this little trick. On most mice, the scroll wheel is a button as well as a wheel. Click on links using the scroll wheel, and the browser will open that page in a new tab in the background without taking focus away from the current page.
I find this extremely handy when browsing results from a search engine. As you visually scan through the search results, click the links that look promising using the scroll wheel. The browser will set to work to load those pages in the background as you continue to scan. After you've got a good batch of pages loaded in your tabs, you can skip through the tabs quickly.