Cody (Various towns) - Job advances (The GM Option will NOT work, nice try though
)
Sera (FM) - AP reset
Coco (Henesys) - Maxes skills, you may need to do this twice if your 4th job skills aren't maxed.
Spinel (All Towns, FM) - Universal warper.
If you scroll to the very bottom and click "Ellinia" she will warp you to a GM Map, where you can change your char's eyes, hair, and skin.
YOU WILL NOT LOSE ITEMS IF YOU CLICK HER.KIN (GM Map) - Changes hair, skin, eyes for male characters
NimaKIN (GM Map) - Changes hair, skin, eyes for female characters
Amos (FM) - Boss Warper
Mr. Moneybags (Henesys) - Sells many rare items (i.e. Flaming Katana, Umbrellas)
Nana(K) (Kerning City and FM) - Sells pets, pacifier, some pet accessories and dragon marbles (they work on all pets)
Mr. Thunder (Perion) - Sells chairs
Mr. Smith (Perion) - Sells fame (1k for 100 fames)
Duey (Various towns) - Sells scrolls
Branch Snowman (Happyville, FM) Sells Thief equips/weapons/stars, white scrolls, dragon stones, transmorphing potions, etc.
Bucket Snowman (Happyville) - Sells various potions, mainly buffers (i.e Onyx Apples)
Spindle (Henesys) - Sells rare NX
Maple Claws (FM) - Sells more rare NX (i.e Janus, Sachiel, Veamoth sets)
Fredrick (FM) - Sells various goods such as Onyx Apples, Smegas, Draco, Saddle, Gachapon Tickets, and Elixirs.
Ueriba (FM) - Sends you to PVP map
Rupert (FM) - Sells warrior armour
Mia (FM) - Sells Gold, Silver, Bronze bags of Money
Melias <Armor Seller> (Aquarium) - Sells Silver Mane, Hogs, and Saddles
Tory (Henesys Park) - Sells pet name tags
Thomas (Henesys) - Allows you to craft FaceStompers
Spiegelmann (Various towns) - Warps you to Omega Sector
JM from tha streetz (Kerning) - Made me go naked
Goldstein (Lith Harbor) - Increases buddy capacity (
NOTE if you want to increase your buddy capacity and the amount of slots you have is 25, you type 40, NOT 15)
I think I got all of them, list an NPC if I missed one.