We've gone to the Arrowhead Crystal Mine a couple of times now, and plan to keep coming back. This is a working mine, and they bring new stuff up all the time. You can just walk around and find beautiful quartz crystals, or you can dig them up. For a bit more money, they will excavate a pocket from the mine and set it aside for you, and you can dig through it and find breathtaking clusters of crystals. The guys are friendly and helpful, and you are certain to find something that makes the trip worthwhile. When you dig them up, the crystals are covered in a rusty looking deposit, but soak them for a while in an acid solution (we found the stuff you get to take iron stains out of laundry works great) and they will be transformed. Many of them are as clear as glass!
Definitely call in advance, as they are closed some days, so they can work the mine. This is a great place for families, but I would not bring any small children- you'd spend all your time watching them, because there are too many ways they could hurt themselves.