Just to start off with, no matter how cheap or expensive your jack is, never trust it to support the car. If you're going to be under the car, have it resting on jack stands.
With the disclaimer out of the way, I'm a believer in buying quality tools the first time and being done with it. As such I bought (and recommend) the AC Hydraulics jack. It has the best reach of any jack I've never used and it of the utmost quality.