Next-gen memory cards are all the rage these days, and the GameCube already has a solid option with 8BitMods' MemCard Pro GC.
Bitfunx's GCMCE is now available and is based on the open-source Flipper Memory Card Emulator project.
According to the product page, it "allows users to store an unlimited number of game saves, fully leveraging modern storage technology and breaking the limits of traditional memory card storage capacity."
The GCMCE supports MicroSD cards from 1GB to 500GB, and is fully compatible with Swiss homebrew software, as well as the FlippyBoot ODE. Game ID detection is also supported.
The card costs $29.99 and works with all GameCube models and RVL-001 model Wii systems.