I too have used the Pocket Light Meter app, and can tell you it's proven very accurate. You do have to learn to use it, however, as it has a large spot meter in it where you click on a spot and it averages the light based on the spot. So if you have that pointed on a particularly dark or brightly colored area, it will give you and inaccurate reading. The spot is too large to use as an accurate spot meter and too small to use as a typical reflective meter. However, the display reacts to it, so it'll give you a example of about what you can expect.
Pocket Light Meter is also only for iPhone. That's part of what makes it so accurate (they can tune the software to the camera). I've even used it for slide film with reliable results. For Android phones, I haven't found one as good and easy to use. Though there are several that are good enough for most cases. I can't recommend any, because in my 6 months with a Android phone (which I really miss the keyboard on because they are far superior to the ones on iPhones), I went through several and never found one that stood out above the others.
I own several cheap light meters, and they're all based on selenium cells. Selenium loses sensitivity as it ages, so none are particularly accurate, but all are fairly consistent. So if I set the ISO on the meter to 200 while using 400 speed film, they work pretty well. Though really, the phone apps are more accurate and easier to use. Unless you find a really good bargain (which I've run across a couple, so they're out there), you're going to wind up spending a pretty penny for a good, easy to use, accurate light meter. Plus there are so many different styles (incident, incident with flash, reflective, spot, and combinations there of), that you'll be best off using a free app until you find out what kind you want to use, as they all have pros and cons.
