Anybody have a idea what to use this plate for?  Its 1"thick and Stainless Steel but I'm not sure what grade.

end table top

Bottom of a welding forge

Upsetting plate for the floor.

Fly swatter for JeremyK's hammer in's

Is it flat? Use some spray on glue to attach a bit of sand paper and use if to sand things flat. ;)

paper weight

If it's straight, use it for a lay-out table and setting 4 legs true. If it's not straight, you can use it for anything, some mentioned above.

24"x24"x1 is around 162# depending on alloy  (160# 410, 164# 304)

Surface plate

Cook totrillas on it.

Griddle, unless it is a free machining alloy with lead added.  Tortilla press for big tortillas, counterweight, non rusting boat anchor, sculpture, target, gong,

That's a proper manly hot plate right there!

If non magnetic, sell it for scrap and buy something you can use.