If you live in a city: Zipcar (Disclosure: Promotional link - if you sign up through this, we both get a $25 credit)
Saves a lot of money and stress. I don't worry about registration or car insurance or gas prices or parking. When I need a car, I pay a pre-determined rate, and then stop worrying about it. Warm fuzzy bonus: Positive externalities in (less land allocated to parking)+(less traffic)+(fewer CO2 emissions).
I've been bike-only for 10 years, with the option to borrow a car from family a 20 minute bike ride away. I signed up for zipcar a year ago after I really wanted a car for something and the family spare wasn't available.
In the year since then, I've looked into using the zipcar for things probably 5-10 times, and rejected it every time. I'm faced with a choice like: do I walk 10 minutes to the car, then borrow it for an hour for $10, then walk 10 minutes back, or just do the errand on a bike? Or, do I borrow the zipcar for a few hours (where the walking time doesn't matter as much), but it's $30? Nah, I'll do things some other way.
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: