A) - Age of Empires 3
B) - Boktai 2
C) - Chrono Trigger DS
D) - Dragon Quest IV
E) - Elite Beat Agents
F) - Final Fantasy 6
G) - Ghost Trick
H) - Half-Minute Hero
I) - Izuna: Legend of the Unemployed Ninja
J) -
K) - Kingdom of Loathing (do MMOs count, despite added content?)
L) - Legend of Zelda: A Link to the Past
M) - Metroid Prime Trilogy
N) - New Super Mario Bros U (would it count despite Yoshi's Island?)
O) - Ouendan 2 (would this count, despite it being known in japan as Moero! Nekketsu Rhythm Damashii: Osu! Tatakae! Ouendan 2. the internet knows it as the former)
P) - Pikmin 2
Q) -
R) - Rhythm Heaven/Paradise (JPN: Rhythm Tengoku Gold)
S) - Spelunky
T) - Terraria
U) - (The) Urbz: Sims in the City
V) - Vib-Ribbon
W) - Warioware: Twisted
X) -
Y) - Yoshi's Island
Z) - Zombies (ate my neighbors)
Notable mentions: Etrian Odyssey IV, Azure Dreams, Mega Man Battle Network 3, Pokemon Mystery Dungeon: Explorers of Sky, Banjo-Kazooie, Shantae: Risky's revenge, Temple Run, Holy Invasion of Privacy, Badman. What did I do to deserve this?. Prinny: Can I really be The Hero?, Super Mario All-Stars, River City Ransom (known as Street Gangs here in UK/EU), BlazBlue: Continuum Shift Extend, Puzzle Quest, Pokemon Puzzle Challenge, Mario&Luigi: Superstar Saga, Paper Mario: The Thousand-Year Door and Kirby: Triple Deluxe, Super Star/Fun Pak -or- The Crystal Shards/64.
trying to think of a Q and an X is hard. don't even own anything like Xenoblade to cheat.