Here are the levels of some LOTR people taken from "Lords of Middle Earth" (MERP):
Balrog: lvl 36 - Maia Fire Spirit.
Gandalf: lvl 40 - Maia (Istar), Mage/Magician, "Gandalf the Grey".
Gandalf: lvl 50 - Maia (Istar), "Gandalf the White".
Saruman: lvl 50 - Maia (Istar), Mage/Alchimist, "The White Wizard".
Arwen: lvl 15 - Half-elf Bard, daughter of Elrond, wife of Aragorn.
Elrond: lvl 65 - Half-elf Animist/Cleric (Bard, Lay Healer, Fighter) of Imladris.
Galadriel: lvl 60 - Noldo Bard/Mystic (Seer), Queen of L?rien.
Legolas: lvl 8 - Sinda Warrior/Fighter, a young Legolas around T.A. 1640.
Legolas: lvl 28 - Sinda Warrior/Fighter, at the time of LOTR.
Aragorn II: lvl 27 - D?nandan Ranger, Member of the Fellowship.
Aragorn II: lvl 36 - D?nandan Ranger, as King Elessar.
Boromir: lvl 20 - D?nandan Warrior/Fighter, Member of the Fellowship.
Faramir: lvl 24 - D?nandan Ranger, married Eowyn.
Theoden: lvl 24 - Rohir Warrior, 17th King of Rohan.
Nazg?ls: lvl 32-60.
Bilbo Baggins: lvl 9 - Hobbit Scout/Thief, Ring-Bearer.
Frodo Baggins: lvl 12 - Hobbit Scout/Rogue, Ring-Bearer.
Peregrin Took (Pippin): lvl 8 - Hobbit Warrior/Fighter.
Samwise Gamgee: lvl 9 - Hobbit Scout/Thief, Ring-Bearer.
Gimli: lvl 8 - Dwarf Warrior/Fighter, Member of the Fellowship.
Gimli: lvl 21 - Dwarf Warrior/Fighter, "Elf-Friend", Lord of Aglarond.
Taking the HARP power curve (discussed in another topic) into account, I would say that highest levels NPCs (Balrogs, Istari, Nazg?ls) should be around level 30, powerful NPCs around level 20 (25-30 for highest level Elves), and Members of the Fellowship (except Gandalf) between levels 4 and 14.
Basically divide every level given in MERP by 2, with an upper limit at level 30.