Here's the final 1991 list, by NASA's Lunar Exploration Science Working Group, of the ranking of the 14 top-ranked instruments for Lunar Observer -- only the top 9 of which were in its strawman payload:
(1) Gamma-ray spectrometer
(2,3) A tie: laser altimeter and farside gravity mapping subsatellite
(4) Visible/near-IR mapping spectrometer
(6) Ion mass spectrometer plus electron reflectometer
(7) X-ray spectrometer
(8) Geodetic camera (100 meters/pixel)
(9) Thermal IR spectrometer
(10) Mapping camera (15 meters/pixel)
(11) UV spectrometer
(12) Second magnetometer (presumably on the subsatellite to help look for a metal core)
(13) Microwave radiometer (for an attempt to measure heat flow)
(14) Neutral mass spectrometer
A list the year before made by a separate NASA group was identical, except that the second magnetometer was replaced by a receiver to see how much radio-astronomy interference there was on the Moon's farside.
After the cancellation of LO, NASA made a tentative attempt to replace it with two smaller "Lunar Scout" satellites. The first would have carried X-ray and neutron spectrometers (the latter for polar ice), a laser altimeter, and a high-resolution stereo camera capable of doing the jobs of both the geodetic and mapping cameras above. The second would have carried a gamma-ray spectrometer and VIMS, and the two satellites would have tracked each other for farside gravity mapping. Congress quickly kiboshed this in the process of spitting all over Bush Senior's entire super-expensive Space Exploration Initiative.
Notice that most of these instruments are scheduled to be carried by SELENE-1, Chandryaan-1, and/or Chang'e -- along with some additional instruments. The missing ones seem to be a thermal IR spectrometer (although a new LPSC abstract says that the multichannel IR radiometer on LRO, intended to map polar cold-trap temperatures, can also do some of the compositional mapping work of such a spectrometer), and a heat-flow microwave radiometer (unless Chang'e's MWR, intended to map regolith consistency, is sensitive enough to attempt that as well. This goal is something of a gamble anyway.) By the way, the lunar impactor that the Indians now intend to add to Chandrayaan will carry a mass spectrometer, as well as a descent camera. If they're smart, they'll crash it into Aristarchus.http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1233.pdfhttp://www.lpi.usra.edu/meetings/lpsc2006/pdf/2406.pdfhttp://www.lpi.usra.edu/meetings/lpsc2006/pdf/1704.pdf