But you don't have to take my word for it:
Prominent appearances since: Eternal Sunshine of the Spotless Mind, Sin City, Happy Feet, Happy Feet Two, Wilfred (TV series)
Post-LotR Analysis: Mark Hamill Syndrome.
Prominent appearances since: Jeremiah (TV series), 24 (fifth season)
Post-LotR Analysis: Arguably the most famous member of the cast before the films were made thanks to Rudy, his legacy was only bolstered by playing Sam, and so probably didn't have much more to prove anyway.
Prominent appearances since: Equilibrium, Troy, National Treasure, The Island, The Hitcher, Percy Jackson & the Olympians: The Lightning Thief, Mirror Mirror, Game of Thrones
Post-LotR Analysis: Became hugely in-demand for supporting roles, and always steals the show; is probably responsible for the early interest in Thrones. One of the biggest winners by far.
Prominent appearances since: The Aviator, Babel, The Good German, Notes on a Scandal, I'm Not There, Elizabeth: The Golden Age, Indiana Jones and the Kingdom of the Crystal Skull, The Curious Case of Benjamin Button, Robin Hood, Hanna, Blue Jasmine
Post-LotR Analysis: Already a critical darling before her appearances as an elf, Blanchett's career skyrocketed afterward and is arguably the greatest beneficiary of the whole cast. She has two Oscars to show for it, after all.
Prominent appearances since: Pirates of the Caribbean trilogy, Troy, Kingdom of Heaven, Elizabethtown, The Three Musketeers
Post-LotR Analysis: Enjoyed a huge boom and unexpected huge success in another trilogy as the most natural of the movie stars to emerge from Middle Earth. Has struggled since then to become relevant again, however. (I remain a huge fan.)
(Peregrin "Pip" Took)
Prominent appearances since: Master and Commander: The Far Side of the World
Post-LotR Analysis: Like most of the other hobbits, Boyd was a tough sell outside of his hairy feet.
Prominent appearances since: Garden State, The Day After Tomorrow, The Aviator, Ratatouille
Post-LotR Analysis: Completely unnecessary.
Prominent appearances since: Attack of the Clones, Revenge of the Sith, Charlie and the Chocolate Factory, Corpse Bride, The Golden Compass, Alice in Wonderland, Season of the Witch, Hugo, Dark Shadows
Post-LotR Analysis: Was completely rediscovered and recognized as the treasure he is.
Prominent appearances since: 13 Going On 30, King Kong, The Prestige, Flushed Away, Inkheart, Rise of the Planet of the Apes, The Adventures of Tintin, Arthur Christmas
Post-LotR Analysis: Became a bloody rock god.
Prominent appearances since: X-Men: The Last Stand, The Da Vinci Code, Flushed Away, Stardust, The Golden Compass, The Prisoner (TV mini-series)
Post-LotR Analysis: Modest, and certainly he had already entered pop culture as Magneto, but who's to argue with Leigh Teabing???
(Meriadoc "Merry" Brandybuck)
Prominent appearances since: Lost, X-Men Origins: Wolverine, FlashForward (TV series)
Post-LotR Analysis: Did I say Andy Serkis became a bloody rock god? Dominic Monaghan became the bloody rock god. Arguably far better known now for his role as Charlie Pace.
Prominent appearances since: Hidalgo, A History of Violence, Eastern Promises, Appaloosa, The Road, A Dangerous Method, On the Road
Post-LotR Analysis: As far as disappointments go, his is a relative one, but it certainly go that much further to prove how the stars aligned for a role that originally went to someone else.
Prominent appearances since: The Princess Diaries 2: Royal Engagement, One Night with the King, In the Name of the King: A Dungeon Siege Tale
Post-LotR Analysis: Already a well-established character actor, he's another veteran who had very little to prove.
Prominent appearances since: Jersey Girl, Reign Over Me, The Strangers, The Incredible Hulk, Robot & Frank
Post-LotR Analysis: Low-key, as with several others.
Prominent appearances since: The Matrix Reloaded, The Matrix Revolutions, V for Vendetta, Happy Feet, Transformers, Transformers: Revenge of the Fallen, The Wolfman, Legend of the Guardians: The Owls of Ga'Hoole, Transformers: Dark of the Moon, Captain America: The First Avenger, Happy Feet Two, Cloud Atlas
Post-LotR Analysis: Like McKellen, Weaving had already entered pop culture as Agent Smith, a role he'd continue simultaneously with his appearances in Middle Earth. But playing Elrond was unquestionably a terrific way to solidify the significant upturn in his career.
Prominent appearances since: Seed of Chucky, Deadwood (TV series), Halloween, Halloween II, Bad Lieutenant: Port of Call - New Orleans, Priest, Curse of Chucky
Post-LotR Analysis: Continued being paid to be creepy.
Prominent appearances since: Gothika, Wimbledon, Valkyrie
Post-LotR Analysis: Didn't wildly benefit.
Prominent appearances since: War of the Worlds, I, Frankenstein
Post-LotR Analysis: Surprisingly little effect.
Prominent appearances since: The Chronicles of Riddick, The Bourne Supremacy, Doom, Out of the Blue, Pathfinder, Star Trek, Red, Priest, Dredd, Star Trek Into Darkness, Riddick, Almost Human (TV series)
Post-LotR Analysis: Unquestionably one of the big winners, although it took a little while. Gained more fans as the second actor to portray Leonard "Bones" McCoy.
Prominent appearances since: Van Helsing, The Proposition, 300, Australia, Public Enemies, Legend of the Guardians: The Owls of Ga'Hoole, 300: Rise of an Empire
Post-LotR Analysis: You probably know his voice better than his face, but Wenham is certainly one of the more surprising winners from the cast.
Prominent appearances since: One Night with the King, Running Scared, The Last Airbender, Fringe (TV series)
Post-LotR Analysis: As Walter Bishop in Fringe, Noble gained new genre significance and his true lasting legacy. My favorite veteran because of it, actually.
(All images via IMDb)