If you have an iphone or other smartphone, you've probably discovered that there are quite a few astronomy apps out there. Most of them cost a few bucks, but there are some pretty cool free ones out there. Here's what I have downloaded to my iphone that you should check out for yourself:
Exoplanet Database: This is an awesome app if you're into exoplanets! It's a database with information about all the different exoplanets that have been discovered, and includes size, period, distance, and other useful information. You can read news about exoplanets, view where any exoplanet is located in the galaxy, make handy graphs of exoplanet properties, and even get links to scientific papers about the exoplanets. The coolest part about this app… it sends a text message to your phone every time a new exoplanet is discovered!
APOD Viewer Lite: An application that lets you view the astronomy picture of the day. It shows you the image, explanation, and lets you look back at previous images. Very nice app to quickly view today's APOD.
NASA: Basically this is NASA.gov in app form. You can find news, launch schedules, pictures, videos, telescope info, and anything astronomy you can imagine. Excellent educational app.
ArXiv: This app allows you to search the astrophysics arXiv for scientific papers, and download the pdf to your iphone (using a pdf reader app). This is more for the serious astrophysicists, but anyone can peruse through the papers and maybe you'll find something interesting.
Galaxy Collider Lite: A cute app that shows you what would happen if two galaxies collided. I'm not sure how scientifically accurate the simulations are, but it's cool to watch the galaxies interact regardless. You can set the number of stars, mass of the galaxies, speed of collision, etc. and observe how that changes things
If you've discovered any other cool free apps, post them in the comments section below! Also feel free to leave your opinion about different non-free apps as well!