My two all time favourites are the Gym Music from Pokemon Red/Blue and the Gym Music from Pokemon Gold/Silver. I used to just have my Gameboy Colour and earphones with me at one point to listen to those. Never found better pump up music.
There's too many to name. From Pokemon I'd have to say Cynthia and Steven's Pokemon theme along with Per Aspara Ad Astra from ORAS and the Kahuna battle theme from SM. I also really love the intro music for Fire Emblem Fates and some Remade Mario Kart theme tracks such as N64 Rainbow Road and GCN Baby Park.
Ok this one is tough haha I've got so many songs that I enjoy especially animal crossing's but here are few which I love and I'm sure not a lot had listened/played to these (hopefully you guys did ):
the stone tower temple music from majora's mask has gotta be my favourite. the zelda series as a whole has an amazing ost along with the soundtrack to wild world, which always drops a huge nostalgia bomb on me when i hear it.