You'll be wanting some of the following:
Super Mario Sunshine,
Zelda: The Wind Waker,
Zelda: Twilight Princess,
Fire Emblem: Path Of Radiance,
Super Monkey Ball 1&2,
Mario Kart Double Dash!!,
Billy Hatcher and the Giant Egg,
Smash Bros. Melee,
Soul Calibur II,
Metroid Prime 1&2.
That would be the beginnings of a very decent collection. Good thing you already have Chibi Robo as that's one of the rarest PAL games and will set you back a bit, ditto MGS: Twin Snakes. I haven't played them so can't recommend them, but DK: Jungle Beat and Killer 7 are also apparently excellent.
Where to get them? Game no longer stock them and GS are cutting back significantly with few stores now carrying GC games. Most branches of CEX still have some, but it's hit and miss as to what you'll get. Local independent stores or the internet are your best bet. As for price, they vary from a couple of quid (Prime, Billy Hatcher) to £20+ (Baten Kaitos, Twilight Princess) but there's nothing that runs into the hundreds. It's a fairly cheap machine to collect for.
Owned: NES, SNES, N64, Gamecube, Wii, Game Boy, Game Boy Color, Game Boy Advance SP, DS Lite, 3DS, Master System II, Mega Drive II, Saturn, Dreamcast