USB I2C Dongles & Drivers

YS-CH341T

A basic USB to I2C dongle is still available on EBay. The  drivers currently only available for Windows PC's. They work on 32 or 64 bit Windows but only with a 32 bit JVM. A relatively cheap device that will work with most I2C devices. It does not support clock-stretching but slowing the speed usuall allows the device time to work. Check the I2C device table for devices that don't work with the CH341T. The driver software can be quite difficult to find so I have put a copy of the driver on Source Forge that seems to work on a range of Windows operating systems.
Software and hardware installation instructions

UMFT4222EV

A relatively new device and more expensive than the YS-CH341T but supports clock-stretching. Available from 'FTDI Chip' in Glasgow. Software and documentation is available for an expanding range of operating systems. The support is excellent. I have put a version of the driver on Source Forge but check the FTDI web site for more up to date versions.
Software and hardware installation instructions