The perfect car is a taxi. Or even better, a network, equidistantly placed all over the city in anticipation of your need for them. You call a number, and one arrives. But taxis can be improved and here are my thoughts.
Let us know when there's a vacant taxi
Some occasions call for hunting down a taxi rather than calling on on your phone. I'm not sure what differentiates these occasions from one another, but they are clearly distinct in my mind. I never hesitate in deciding between the two... the answer is always clear, even if the method of arriving at the answer is not entirely clear.
Better paid drivers
Being a taxi driver shouldn't be such a huge gamble for a career. There should be part-time taxi drivers, drivers who are going through college, pregnant women drivers who still want to hear what people are doing out on the town (this coincides with my idea for a pregnant woman designated driver network... but I can't tell if that's offensive or not), even highschool drivers. Drivers should determine their own pay and when finding a taxi both the vacancy of the car and the price of the car should be made apparent. A free market for taxis. Likewise, it should be easier to get a particular driver when ordering a taxi... maybe there's a menu when calling to put in a particular driver's number... and you can make a decision based on that.
Better taxi technology
RSS feeds for everywhere a taxi has picked you up and dropped you off. In-taxi "rate your ride" display. Statistics on your driver's rating. Better credit card integration. Perhaps there should be a button for "need to get there fast", "want to take the scenic route", and "would prefer not to have conversation".
Taxis need to serve alcohol, for one very good reason: why not? Limos serve alcohol, so what's the big deal? Whether it be little bottles of alcohol, or a bartender in the front passenger seat, I don't really care.
A new "passenger seat bar" contraption may need to be invented. One that holds ice, tonic, soda, limes, cherries, and an assortment of essential liquors: vodka, gin, whiskey, beer, and wine. The market for these new contraptions may be small (given that most people don't have need nor license to have a full bar in the passenger side foot area, but it would definitely be fun to design and could be an appropriate challenge for someone like the guy who designed the Aeron chair, or the guy who designed the Palm Pilot.
I often get in a taxi and find myself in need of advice. Who better than a taxi driver, or rather on-board psychologist/mentor/psychiatrist to give this to you? They are impartial, must resort to brevity, and completely wise. They have been on a million taxi rides, been privy to a million different situations but in such a way that they were able to find patterns in the variety, increasing their wisdom beyond normal human means. You give them a 2-minute run-down of the situation at hand. They draw immediate conclusions about your condition "you seem like a nice guy", "don't be too nice", etc. They ask a for a few key details that are necessary to paint the entire picture, "how much do you make?", and "was the woman in the taxi earlier your girlfriend?", and then they pause... what are they thinking!... until finally, "no, I don't think it's right", or "yes, you should do it." And then, voila, you've arrived at your final destination and he whips up a prescription to take your nerves down, and hands you a whiskey on the rocks as you step out.
On-board Private Detective
Some cases may be too difficult to solve during the duration of the car ride. This is where the on-board private eye comes in. They can look further into something, tail someone, bribe someone, get tickets to a sold out show, and find out where your friend goes for happy hour. In serious cases, they can even be hired to tail you... observe from afar and figure out why people don't like you, pinpoint the exact moment that your days take a turn for the worse, and let you know when the best time to "happen by" the bar is.
I do see that the front seat is getting crowded. Some people may be able to fulfill the psychologist and detective roles together, others may need to take advantage of that uncomfortable third seat belt area where the stick shift often goes.
That's all I've got for now. This idea is evolving by the day though. What am I missing?