Taxi Magic is a fantastic app that's totally legit. Open the app, use your location to book a cab and within 5 minutes it's there. It's Luxor Cabs who are fully licensed and use computerized dispatch.
I tried UberCab once and it was a nicer car but the experience was no better than Taxi Magic, and significantly more expensive to get around town.
I hate non-metered cabs. Taxis are one place where regulation is good. We all know what it's like to deal with a shady taxi driver. The tendency is to gouge vulnerable travelers, not to set lower prices. The consistency that regulation offers is the most important.
I also can't believe the complaints about the taxis in SF. The cab companies are downright excellent when you actually call, and plentiful on the streets.