The easiest way to connect peripherals to the Beagleboard is by USB. The revision B5 board that I'm using has a single USB OTG port. Connecting a USB hub allows multiple devices to be used.
The USB OTG port can be put into host mode using a special USB mini A cable, or by shorting two of the pins together.
This allows a more readily available mini B host cable to be used:
A powered hub is necessary as the OTG port can only provide 100mA of current - this isn't enough for hungry items like a webcam and wifi dongle:
Unfortunately there's a bug on the Beagleboard that prevents some USB devices (like the webcam) from functioning properly with the USB OTG port. I've posted to the Beagleboard mailing list for a solution.