CNC simulator recommendations

I know this is probably a common question but I've tried searching
these archives under "CNC Simulator" and I'm not hitting anything
(or maybe they busted the search tool with this new forum layout).

I'm new to CNC and I'm going to be bringing a retrofitted but busted
BP machine back to life. While I'm waiting for the machine to show
up as a learning process I'm doing some simple designs and reading
them into SheetCam and then generating the output G codes.

I understand that there are some pretty good (and free) CNC
simulators available that would let me test this code but I haven't
been able to find them.

Can someone point out links to some of the simulators?

I'll have to admit, this CNC stuff is pretty fun your first time in-
kind of like your first real girlfriend (heck, maybe better).

Thanks,

Paul T.