I have a monster 2 1/2 ton jack from years ago that kills my back when lifting in and out of the hatch when at the track, so I finally bit the bullet and bought an El Cheapo aluminum jack...but it's a damn good design as far as reaching under a lowered SVT (Spec Focus suspension):
HarborFreight item 92782
The low, curved side plates of the jack frame allow you to center the jack on the side skirt joint (below the front edge of the front door, just behind the front wheels), push the jack all the way in and just reach a perfect jacking point on the box section of the unibody. I haven't tried going in under the front or back bumpers, but I use it mostly for swapping tires on one side of the car...ramps are my preference for simple stuff like oil changes. [race]