Pete,
Just make sure whatever you buy lifts to around 20" or so.
I had a 2.5 ton "speedy lift" jack that gave out in a matter of months. It was spitting fluid everywhere whenever I used it. I doubt that it deserved the 2.5 ton rating.
Now I have a 3 ton Craftsman that is BEEFY. The wheels are twice as big, the body is twice as wide, and the handle is twice as long. This thing is built like a brick crud house. Its not as fast as the "speedy lift" jacks, but man this thing could lift a bus! Its not on the Sears website, but they sell it in store for $70. It has an advertised lift height of 19.75". Great deal and I couldn't be happier. If you're looking for light and fast this is not your jack, however. This gets high marks in safety and strength though.
Edit: Found it on the site...
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00950186000&subcat=Lift+Equipment
Another note - Sears sells a high lift "SUV Jack" that claims 21" lift. Compared to the one I mentioned above it was actually lower. Plus it looks exactly like the $35 one Walmart sells. It is also the same design of the one that I had give out on me. BEWARE. Here's the link...
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00950143000
You can't tell from the pics, but the first jack I showed a URL for is literally about twice as big and much heavier. The product specs show 80 lbs vs 54 lbs. Same price, same material...you be the judge.