For DS:
Kirby Super Star Ultra. Even if you aren't much of a Kirby fan, I would recommend this game because it's addicting, appealing, and well worth it. Once unlocked, there are over a dozen unique games and sub-games filled with bosses and abilities in this side-scrolling platformer. There is even a mode that allows you to play the same levels again as Meta Knight. I practically have nothing bad to say about this game.
Alice In Wonderland. Hear me out on this one. This is actually a charming game with terrific design, gameplay, and music. You don't control Alice herself but rather four unique characters that you switch between frequently to help her solve puzzles and engage in combat. You can go on to explore the artistic world and find concept art and other content. You may quickly discover that just about everything in this game is clever and likable.
Fire Emblem: Shadow Dragon. This game centers around Prince Marth's battle to free his homeland and rescue his kidnapped sister. I found it a solid game for its kind, very tactical and quite difficult. It is presented in a way that makes it fun and unique.
I hope you find one that you like. And if you end up looking for a GC/Wii game, here are some suggestions.
For GC:
The Wind Waker
Star Fox Assault
For Wii:
Red Steel 2
Ōkami
Super Paper Mario
The Conduit
Tatsunoko vs. Capcom: Ultimate All-Stars
Metroid Prime Trilogy
GoldenEye 007
Marvel: Ultimate Alliance
Monster Hunter Tri