Way too many favorites to pick from.
Aladdin - A Whole New World (this is one of my favorite love songs ever, not only because it's beautiful and makes you appreciate the wonder of it, but also because it uses harmony to perfection)
Aladdin and the King of Thieves - They're Finally Getting Married (this, I think, is actually funnier than any of the classic Aladdin songs you usually think of)
Out Of Thin Air (another excellent use of harmony, and it expresses Aladdin's inner struggle about his father better than any amount of dialogue, I think)
The Many Adventures of Winnie the Pooh - Tigger's song (you know, the one that goes, "Oneofthemostwonderfulthings about Tiggers, isTigger'sawonderful thing! They're bouncy, flouncy, pouncy, trouncy, funfunfunfunfun!!" etc.)
The Little Mermaid - Under the Sea (one of the most wittily rhymed songs I've ever heard)
Beauty and the Beast - Something There That Wasn't There Before (or whatever it's called, which I like because it shows the progression of this love story, which is more realistic than most fairy tales)
Kill The Beast (you know, the one where Gaston's riling up the townsfolk; I find it rather epic and a bit frightening even to this day)
Brother Bear - No Way Out (one of the best, most emotional and moving songs out of any Disney movie I've seen; it was the perfect choice to use during Kenai's confession, displaying the emotions when we already know the particulars, so that the music and the visuals and what you
know he's saying mingle together into one heartbreaking experience)
I'm On My Way (mainly because Koda sings part of it and it's incredibly cute to see the "brothers" draw closer through the course of this song, but it's also just a really nice, uplifting song)
Treasure Planet - I'm Still Here (tells the story and emotion so well and so effortlessly; when this song got going, that was the point where I knew I loved this movie)
Toy Story - You've Got a Friend in Me (while I don't normally go for country songs, this one has always stood out to me as a wonderful description of what true friendship is)
Toy Story 2 - When She Loved Me (T_T most heartbreaking song I've ever heard in a Disney movie; it even made Tom Hanks and Tim Allen cry!)
Monsters, Inc. - If I Didn't Have You (another really awesome song about friendship, a great depth of emotion masked by a whimsical exterior)
Bolt - I Thought I Lost You (a really uplifting friendship song, made even more powerful because it was sung by the voice actors for the two main characters)
Marry Poppins - uhhh, basically all of 'em ._.
...that's all I can think of for now.