I know it's not what you wanted to hear, but your best bet is to level the floor. It's dangerous to have your woodworking machinery on a slope that might cause it to tip or rock unexpectedly, even if you have some means of adjusting the legs to match the uneven floor. Also, it will be far easier to move the machines around on a level floor, and you're less likely to trip or stumble when feeding stock or moving large pieces around the shop. If, however, you need to level a machine that doesn't get moved much (such as a table saw), feel free to use whatever means you can find. Shimming the base with wood shims, or using furniture levelling feet will work. Keep in mind that the sloping floor is indicative of more serious foundation problems that may need to be addressed. You can always fill in the low spots with portland cement. I made a pad for my table saw, so I can work outside when the weather's nice. I'm sure others will have even more options.