Marking up content on web sites to indicate structure is a good idea for enhancing its attractiveness to search engines. Google's new Structured Data Markup Helper lets you identify specific types of data on your site and then shows you the HTML you should use to embed that structure on your page.
Marking up your content makes it more likely it will be used by Google's Knowledge Graph and featured in Google Now. The webapp covers eight common types of sites and suggests information related to them.
Google has also enhanced its Data Helper tool, a simpler tool which lets you highlight data on a site with your mouse to indicate its structure. That's easier to use, but doesn't make permanent changes to your site (and won't assist with any rival web crawlers or analysis tools).