I'd like to start off by saying that, no, I don't believe in any kind of real science behind crystals. I go to a store in my city that sells them and smile politely when the employees start talking about ions and healing energy and other things I interpret as pseudoscience.
But I'm a sentimental person. What I like about crystals is that they each have a specific meaning. I like to choose a different crystal every morning and let the meaning behind it guide how I approach my day. If I'm doing something stressful, I bring blue tiger's eye, which symbolizes "going with the flow." If I'm spending time with friends or going on a date, I bring rose quartz, which symbolizes compassion and love. If I'm having a bad day for DR, I wear black tourmaline, which deflects negative energy, or hematite, which is meant to help you feel grounded.
Again, it's very unlikely that these crystals actually do anything. It's the symbolism that helps. Throughout the day, I remember that I'm wearing one of them and it helps focus my thoughts on the meaning - compassion, being grounded, honesty, etc. It's a bit like a placebo.
They're also pretty, so people don't give you strange looks if you wear them.
Anyway, this is something that helps me. It's obviously not for everyone, but I thought I'd share in case it might help someone else, too.
My favourites are hematite, amazonite, sodalite, rose quartz, blue tiger's eye, black tourmaline, and turquoise.