BarTab is a popular add-on for Firefox, preventing tabs from a previous session from loading until you activate them. Anyone who keeps 20+ tabs open knows the primordial sadness of watching one's browser struggle with the load of restoring such a large number of tabs simultaneously. Now, Chrome users can enjoy the benefits of the add-on with an extension called FooTab.
It's currently in beta and not as polished or stable as BarTab, but right now it's your best option if you're looking for relief from mass-tab-loading misery. According to creator "mike-sf-outlook", FooTab is "much less sophisticated and powerful" than its Firefox counterpart, but the way it works is fairly straightforward.
It blocks web traffic for 10 seconds after the browser is loaded, beyond which it will monitor all currently open tabs. Only when one of these tabs is activated will it load its content, saving you (and your machine) the burden of it otherwise.
As mentioned, it's definitely not the most rock-solid extension, so be prepared for a bit of roughness around the edges.