78L05 from Digi-Key or 7805 from Radio Shack (a higher
power capable package, if you heat-sink it). See the
pinout at www.national.com
(part search for datasheet).
These are super easy to use, VIN to ignition 12V, VOUT
to the MAP sensor supply pin, common all the grounds
and away you go. Maybe add a bypass capacitor to the
output just for quietness' sake, a 0.1u ceramic. I'd go
and bare-wire it, epoxy the regulator right to the MAP
sensor body and put the whole thing in a project box
with a tube for the manifold pressure and 12V, GND and
output. The National datasheets should have simple
application schematics for you too.
You need to find the documentation for whichever MAP
sensor you use, to determine the endpoint voltages,
they vary slightly between versions. Here is one 'sheet
off Delphi's web pages...