I got LEGO Indiana Jones to hack the console for homebrew and then discovered it's a really fun game. Also if you have a balance board then Shaun White Road Trip is totally worth it (probably super cheap in a bin, too).

Lego Star wars is a awesome co-op game if you have somebody to play it with.

I recently finished MadWorld which I can recommend aswell especially if you're into it's style.

Red Steel 2 has amazing sword control.
Just Dance 2 and 3 are both really worthwhile if you like dancing. Also hilarious.

Oh my. I can't believe I left out Red Steel 2. Awesome game.

Here are some of my favorites (listed alphabetically):

Boom Blox / Boom Blox: Bash Party
de Blob
Deadly Creatures
Fire Emblem: Radiant Dawn
Fishing Resort
Geometry Wars: Galaxies
Kirby's Epic Yarn
Little King's Story
Marble Saga Kororinpa
Muramasa: The Demon Blade
New Super Mario Bros. Wii
Pandora's Tower
Pikmin 1 / Pikmin 2
The House of the Dead Overkill
The Last Story

I've also got Xenoblade Chronicles, but it's unopened and therefore unplayed, but it's supposed to be really good.

Thanks everyone for the suggestions! I will definitely be checking out several of the games mentioned. Probably the games I will be getting first:

Metroid Prime Trilogy (loved the original on the GC, never played the others)
RE4
Red Steel
Sin & Punishment 2 (never knew they made another one after the N64)
Xenoblade Chronicles

Whatever you do. Red Steel 2 is better than 1.

No mention of Monster Hunter Tri I am dissipointed.

Oh and Wii Sports Resort is surprisingly fun.

Did not enjoy Monster Hunter Tri at all.

What are you talking about? I mentioned it

Not only that, but you weren't the first person to mention it!

Elmofongo is losing it in his old age. ;)

Alas I seemed to have miss looked your post.

Mad World
Harvest Moon in general