Suction cup phone windshield holder
If you use your iPhone for music in the car this thing is indispensable. I've used 4 different car mounts and this has been the most convenient to attach and change positions of, as well as the one to go the longest without breaking. The bendy arm makes customizing where it is super easy. The gripper isn't precisely engineered to fit the shape of my phone like some others are but this means that it works a lot better with cases and should theoretically work better with various kinds of phones, and still grips in a perfectly satisfactory way. I've never had my phone fall out.
On a related note I strongly recommend getting bluetooth interface for your phone if you get or make calls in the car often.
Mine broke after about a year, as did the other one I tried before. I'm going to try the Wirecutter's recommended one next.
I have often benefited from recommendations for Things I Didn't Know I Wanted.
Given that Less Wrong is a community of unusually intelligent, critical, and self-improvement-focused people, I suspect we can generate a pretty helpful thread of product recommendations — perhaps even a monthly thread of product recommendations.
Rules: