SDXC is the future of SD card technology, with a theoretical maximum capacity of 2TB -- that's 2,048 gigabytes.
At the moment, SDHC cards commercially max out at 32GB. It suffices, but it soon won't. Already camcorders are shooting in 1080p, and it won't be too long before they shoot in 1080p that doesn't look like a haggard mess of modest bit-rate artefacts. Phones, too, are beginning to support not only HD video playback, but capture too.
The technology will be available in smaller SD card formats as well, such as microSD and Sony's Memory Stick Micro M2 cards.
It'll be several years before you'll see microSD cards in the terabytes. But a time will come where a 512GB microSD card will seem like a bitter memory of the past, inadequate for all but the most paltry of storage requirements.