infiniteMPG wrote:
We're about to start tiling a kitchen floor over stripped bare
concrete slab. We're going to be using 18" X 18" tile and we've
started noticing that the floor has quite a few uneven spots in it up
to 1/4" or so. We've heard about leveling compounds but we're kind of
new to this.

Use self leveling concrete, if those spots are large, or even if the
whole floor slopes 1/4" from one end to the other. A level floor will
make much easier installing cabinets, for example.

We already have our cabinets mounted so whatever we use
we need to take that into consideration.

Ouch! Are you going to tile around the cabinets? Bad choice, IMO. Will
be a PITA to install or service a dishwasher,for example, and hope
you'll never have to replace one of the bases. Also, probably you'll
have to make more tile cuts to fit the profile of the cabinets.

Not sure what can be put
down prior to the tile to level the floor better or if something
different can be used to mount the tiles that can take up the uneven
floor?

Again I would use self leveling concrete, and would consider removing
the cabinets and covering the whole kitchen floor with tiles .

If there are only a few lower spots you could just use more mortar under
the tiles there, but there is a potential risk to leave air pockets if
you're not careful.