ARM has made their elegant 32-bit RISC processor core available for licencing to chip manufacturers, who have used it to produce a wide range of very cost effective microcontrollers, packed with lots of peripherals and generally requiring quite simple support circuitry to run. Easy to use, not demanding much space or power, affordable, and bursting with processing power and storage capacity, they seem set to become a popular device in many embedded applications. There's been a lot of hobbyist interest, too, since the devices look like a painless way to add intelligence to electronic devices.
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I2C (aka Two Wire Interface), SPI, PDC (Peripheral Data Controller), SSC? (Synchronous Serial Controller), 1-Wire, Microwire
CAN, Ethernet, RS232, USB, RS485
Compact Flash, MMC Card, SD Card, SmartMedia? Also known as SSFDC
http://www.interfacebus.com/Bus_Design_Top.html has lots of information on busses. http://www.ghielectronics.com/ sell an LPC2114 pre-programmed with an implementation of the FAT filesystem, and device drivers for IDE, MMC Card, SD Card, and Compact Flash, that your master device controls via RS232 or SPI.