Depends...
Is the stud current part of a wall? If so, probably a circular saw & chisel.

If not, and I had access to a radial arm saw, that would be the ticket.

If there were a LOT of them to do, and lacking a radial arm, probably a
jig and router.

If just one or a few, certainly a circular saw and a chisel.

said the following on 2/27/2005 4:44 PM:
How would you go about cutting a notch in a regular 2x4 stud
across the grain, so that the notch is 1.5" into the grain
and 3.5" along it? (i.e. to embed one 2x4 crosswise into
another).

I guess a jigsaw could be used but it seems that there's
got to be a better way. What tool should be used to make
this cut?

RPM