Here's some:
Pallet Town
Route 1
These sum up the fun of starting an adventure.
Kanto Wild Encounter Theme
To me, this is the definitive battle theme of the series. Mostly because I spent a lot of time as a kid playing Free Battle in
Pokémon Stadium.
Goldenrod City / Bicycle Theme
Lavender Town
I love ghosts and anything spooky. Gengar is my favorite Pokémon and Mega. Giratina is my favorite legendary. Halloween is my favorite holiday. Need I go on on why I love this theme?
The Main Pokémon Theme
Too classic to need to explain, do I?
Gym Leader Battle Theme
The first time I ever heard this was on
Stadium and the anime, so this is what I think of when I think of Gym Battles.
Jublife City
This is nostalgic for me (well, as nostalgic as something can be from when you were 16 and are currently in your early 20s). So many good times trading on the GTS.
Vs Rival (Black and White)
This remains my favorite rival theme. I don't know why, it just brought a smile to my face every time I heard it playing through the game.
An Unwavering Heart
I don't remember this theme until I heard it in Y. It's really good. It reminds me of
"Here With You" from my favorite anime,
Future Diary*.
Virbank Gym
I enjoyed the concept of a gym that was also a club and this variant of the classic gym theme was great. Also was the first time we've actually heard a NPC in the games.
Lumoise City
I just love this theme. It just has a great feeling to it. Also, it is the only overworld theme that cannot be overridden by the bicycle. That is the greatness of Lumoise!
Snowbelle City
I do enjoy this theme a lot. It's just pretty.
Hall of Fame (especially the X and Y version)
The Hall of Fame theme had to be in there. That feeling of triumph is spot on. The
X and
Y version of it is the best.
Littleroot Town
Another great example of home town greatness. Plus, this really sets the standard for the remixes we hear in ORAS.
Vs Zinnia
Vs Wally
Both are good, but they are very repetitive, even for video game music, so that knocks them down a bit.
Dig! Dig! Dig!
I was very good at this mini-game, so I have good memories of it.
*Me obsessed with yandere? [sarcasm]No.[/sarcasm]