Google's free fonts are a great way to spice up any presentation or design you're doing, but since you have over 500 to choose from, it's a bit overwhelming. To make the task of selecting a font less daunting, tech blog Digital Inspiration has put together a series of reference posters for easy printing.Google's free front collection can be used without restrictions for any purpose. You can download them for use in Office or Photoshop, as well as Google Docs. The best part is they're open source, which means you can use them for commercial products as well.
Digital Inspiration has already put together reference posters for each font collection, but there's also a guide for customising and making your own. If you're looking to learn a little more about which fonts work best where, check out the previously mentioned Type Connection.
Quick Reference Posters for Google Web Fonts [Digital Inspiration]