I Love reprises where they basically take the whole song again and change the context. I'll cover you is a great example.
In the musical Love Story which played in London the final song was a reprise of the first number called "What Can You Say". It was absolutely stunning. The reprise of Everything we Know in Love Story absolutely broke me to tears.
Some lighter examples, I love how Hello is reprised in Book of Mormon, and Take me to Heaven in Sister Act. Also the reprise of "The Last Time" in the musical of Lend Me a Tenor comes at the most perfect moment.
"Oh look at the time, three more intelligent plays just closed and THE ADDAMS FAMILY made another million dollars" -Jackie Hoffman, Broadway.com Audience Awards
With Every Breath I Take from City of Angels. Act I, it's a beautiful ballad. Act II, it's a heartbreaking duet leading to the inevitable conclusion of Stone's story.
Written In The Stars (Reprise) - AIDA He Lives In You (Reprise) - LION KING The Song That Goes Like This (Reprise) -SPAMALOT (Sure the first one's hilarious, but I personally love this one even more and crack up every time)
"These rabid fans...possess the acting talent to portray the hooker...Linda Eder..." -The New York Times
HE WHISTLED AT ME from Starlight Express - in the original production. I absolutely love the Fairlight orchestrations in the reprise. So good in a very cheap 80s electronic way - just like the show.
I am a firm believer in serendipity- all the random pieces coming together in one wonderful moment, when suddenly you see what their purpose was all along.
Other than cutesy pastiche reprises - often by secondary, sometimes juvenile, couples when the original is sung by the leads - most reprises successfully build from, provide greater emotional impact, and enhance, often very poignantly, the nuance of the original exploration/hearing of the song.
Just one example: Fagin and Dodger's final exit in Oliver, reprising and, precisely as they leave the stage, profoundly underscored by "I Think I Better Think It Our Again" is extremely effective.
'The Other Side of the Tracks' from LITTLE ME. Specifically thinking of the Faith Prince/Martin Short Revival here.....her reprise of this just shortly after the initial slower version is thrilling.
Hairspray: Velma's Revenge in my openion is better then (The Legend of) Miss Baltimore Crabs. now i know that this isnt techinally a Reprise but it basically is.