If you've ever had trouble finding a particular star, planet, or constellation in the sky at night, having your own planetarium could come in handy. Even if you don't have a domed ceiling with a planetarium projector, you can still download a planetarium application for free at Stellarium.org. It comes with a default catalogue of over 600,000 stars (and there's extra catalogues with more than 210 million stars). You can have it connect the constellations together, zoom in, change your location, and more.
Check it out here.