Obviously Tolkien had no concept of character classes when he wrote LOTR, but it is fascinating to try and guess at what class some of the major characters would be had they been rendered as a LOTRO player character.
Burglar: Obviously Burglar Baggins himself would be the inspiration. Frodo may be considered a Burglar. I think Golem would defintaly be a Burglar.
Hunter: Legolas clearly. He is the only definite hunter I can think of. In The Hobbit the Dwarves are said to use bows capably, which I imagin is where the idea of dwarven hunter comes from.
Lore-Master: I can't think of any lore-masters off the top of my head. Faramir says that when he first met Gandlaf he thought he was just a lore master to later realize he was much more. Radaghast and Saruman also fall into this category, but I think Saruman would be a little less "lore masterish" than the other two. I think that maybe Denethor could be considered a Lore-Master, and probably Elrond.
Rune-Keeper: We can all admit that Rune-Keepers break Lore a bit. I really can't think of a good example of a Rune-Keeper. I think that maybe as he started to have more of a mind for power, Saruman perhaps became less Lore-Masterish and more Rune-Keeperish. However Gandalf does seem to "invoke names" in his power, so perhaps the Wizards are a healthy dose of both Rune-Keepr and Lore-Master.
Minstrel: I think that Merry and Pippin could be considered minnies. They both preform a little in combat, but in the story they mostly move others through the words and personalities. They don't really sing THAT much, but I suppose a Minni could move and rally others through speeches as well as song. I also think Grima Wormgtounge would be a Minnie...and evil one no doubt...but thorugh his words and his evil "song" he almost overthrew the King of Rohan. His words clearly have great power. Galadriel also, with her words being able to shake men to their core, could be a Minnie.
Guardian: Gimli is clearly a guardian. I think you could also make a case for Boromir being a guardian, since he used a sword and shield and was literaly a meat sheild to protect others (do his own demise). I also think that you could consider Sam a Guardian. He didn't have a shield, but his nature in the book and the way he acts, and his reasons for fighting when he does....it has Guardian written all over it. He is not flashy or particularly skilled, he is just really tough and has a lot of heart for that which he loves. Guardian in my book. I also think you might be able to call Eowyn a guardian or may a Warden
Captian: I think that Theoden would be a Captian, Faramir definatly, and probably Return of the King Aragorn. These figuers lead and inspire men to great deeds.
Champion: You could consider per-ROTK Aragorn a Champion probably. A whirlwind of front-line destruction at Helm's Deep. You might be able to consider Boromir and probably Eomer as Champions.
Warden: The Rangers as a whole seem to be a mix-mash of hunters and Wardens, primarly Wardens though. I can't think of any main characters that would be Wardens, but the Dunedain definatly seem to be, and also Haldir of course. It is possible you could consider Glorfindel a Warden as well, or a champion, but he's not heavily armored.