Are you looking for a stretch limo or just a car service?
For basic car service (usually a Town Car, sometimes an SUV), I usually use
New Day for personal trips and
Odyssey for business trips.
New Day is similar to Dial7, but a lot smaller and based in my neighborhood, so I find their service to be a bit more personal. But some people prefer Dial7's ubiquity (particularly for airport pickups, where if your driver doesn't show, there's almost always another nearby who can pick you up).
Odyssey is one of a million mid-range services that focus mainly on corporate accounts (others include
Dial Car,
Elite and Fone-A-Car (718-832-4600)). These services tend to have newer and cleaner cars than the Dial7s and New Days of the world, but don't cost nearly as much as the higher end Careys, Boston Coaches and Dav Els. I only use Odyssey because I have access to their web-based reservation system through my work, which saves me tons of time in arranging and expensing the ride. But they've never let me down.
Note that most low-end/mid-range NY car services charge a few bucks extra for inside pickup, where the driver waits inside with your name on a sign and takes your bags. The rates they advertise are usually for outside pickup, where you call a dispatcher when you arrive to get a car number, and schlep your bags to the curb to wait for your car.