If you go into Chrome’s settings, you’ll see a “Manage search engines…” button under the “Search” section. Click that, and you’ll see a list of sites you can search directly from the omnibar. Chrome will add most of these naturally.
So if you enter the URL for, say, Wikipedia, you can then hit Tab, and enter whatever Wiki article you want to find. This saves you the minor-yet-extra step of going to a site’s homepage before finding what you what to find.