And for the tenth top ten list, I've ranked the top ten LEAST likeable Kingdom Hearts characters!! Y'know, those ones that you just can't stand? Enjoy X) (and please don't kill me. I didn't mean to offend anyone!)
10. Zexion
9. Ariel
8. Seifer
7. Xaldin
6. Xemnas
5. Braig
4. Vexen
3. Xehanort
2. Larxene
1. DiZ

The top ten scenes in the Kingdom Hearts series that you should not be afraid to cry at. *SPOILER WARNING!!! If you haven't played all the games, read no further! Ending scenes are discussed!
10. Aqua saves Terra
9. Ven's request
8. Sora and Kairi reunite/Riku as Ansem
7. Xion/Axel showdown
6. Axel's death scene
5. Sora becomes a Heartless
4. Roxas returns to Sora
3. Xion's death scene/358 ending
2. KHI ending
1. KHII ending

My top ten favorite lines from the Kingdom Hearts series. I'm probably missing some but I don't have time to revise the list, sorry.
10. "Hello, bridge!" -Data Sora
9. "Hmph, it's always about your friends, isn't it?"
   "At least I have some!" -Vantias, Ven
8. "Got it memorized?" -Axel
7. "You really do remember me this time? I'm so FLATTERED!!" -Axel
6. "What if everything we've done...What if it was all for nothing?" -Sora
5. "No one would miss me."
   "That's not true!...I would." -Roxas, Axel
4. "Well, there is one advantage to being me. Something you could never imitate.
   "Really? What's that?"
   "Having you for a friend." -Riku, Sora, Riku
3. Kairi's letter (full quote in description)
2. "My friends are my power!/My friends are my power and I'm theirs!" -Sora/Ven
1. "That's not true! The heart may be weak, and sometimes, it may even give in. But I've learned that deep down, there's a light that never goes out!" -Sora

Since Dearly Beloved is, in a way, the theme of Kingdom Hearts and since it's one of my favorite pieces in the whole series, I've dedicated an entire list to it. These are my top ten favorite versions of Dearly Beloved and YES, there are more than ten versions. I know, right? It's insane.
As always, links and reasons in the description.
10. 3D
9. Music Box
8. KHI-reprise
7. KHI
6. Re: Chain of Memories
5. Birth by Sleep
4. Piano Collections
3. 358/2 Days
2. KHII
1. KHII-reprise

Besides having powerful emotional music, Kingdom Hearts also offers a plethora of insanely epic pieces featured in battles and cutscenes. These are the top ten pieces that I believe to be the most epic pieces in all of Kingdom Hearts.
Links to the pieces and reasons for choosing them are in the description.
10. Vim and Vigor
9. Organization XIII
8. Darkness of the Unknown/A Fight to the Death
7. The 13th Struggle
6. Sinister Shadows
5. Dark Impetus
4. The Other Promise
3. Enter the Darkness
2. Fate of the Unknown
1. Another Side

I think many of us will agree that the soundtrack for Kingdom Hearts is, at the very least, beautiful. Yoko Shimomura did a terrific job. (Fun fact: Shimomura is a girl! I did not know this until today!) Here is a list of what I think are the top ten most emotional pieces in the Kingdom Hearts series. Links to the pieces and my reasons for choosing them are in the description.
10. Enchanted Dominion
9. Missing You
8. The Other Promise
7. Riku's Theme
6. Sanctuary
5. Aqua's Theme
4. Dearly Beloved (KHII-reprise)
3. Sanctuary (After the Battle)
2. Roxas
1. Kingdom Hearts Theme

These are my top ten favorite Keyblades from the Kingdom Hearts series. Pictures and reasons are in the description.
10. Rainfell
9. Two Become One
8. Metal Chocobo
7. Bond of Flame
6. Oblivion
5. Fatal Crest
4. Star Seeker
3. Oathkeeper
2. Ultima Weapon (KHII)
1. Kingdom Key

These are my favorite Heartless from the Kingdom Hearts series. Pictures and reasoning in the description.
10. Shadow
9. Bit Sniper
8. Dual Blade
7. Neoshadow
6. Possesor
5. Arch Behemoth
4. Stealth Sneak
3. Phantomtail
2. Unnamed Heartless
1. Wyvern