Also, loading a jack well under its max capacity generally makes for easier operation and greater control (not to mention safety). IMO jacks and jackstands are things you ought not skimp on; your safety is worth spending money on.
Even if you're just taking off the wheels I'd absolutely put jackstands under it just in case something happens with the jack. Things get bumped/etc. and jacks *do* fail (my second fancy floorjack from Griot's went inop last week, prompting me to order something *really* good).
Give some thought to the jack's pad- most jacks come with a steel one. I prefer rubber ones that don't mar up the undercarriage/jacking points. Consider what your usual jacking points will be when choosing the pad (there are different styles).
And also consider how high the jack will have to go. A RAV4 isn't the same as a 'vette, for instance.
This is one of those things that takes a little research and thought if you want to get the right setup the first time.
