Watch the Open Strings online guitar lesson by Jeff Scheetz from Rock Tricks
Sometimes the simple things are the ones that are really cool. Using open strings in your playing is one of those things. Many times it gets dismissed as "beginner stuff" or "too easy", but one listen to country shredder Johnny Hiland and you can see it may come in handy.
You can also hear it used quite a bit by Eddie Van Halen, and Angus Young of AC/DC in different ways. There are tons of classic rock tunes where the main riff is based around an open string lick, like the aforementioned AC/DC's "Thunderstruck" or Led Zepplin's "Over the Hills and Far Away" to name but a couple. Dig in and see what other tunes you can find that utilize this "Under the radar" technique.