Maybe this would work. It's buit around the MAX3421E USB to SPI chip.
Sparkfun also has a shield,
The Arduino USB Host Shield library,
claims support for, quote:
"•Human Interface Device AKA HID. Keyboards, mice, game controllers,
bar code scanners, magnetic card and RFID readers – the list goes on.
Initialization, polling, report descriptor parsing, as well as
reading and sending reports is possible.
•Asynchronous Serial over USB AKA CDC. Devices of this class
provide serial connectivity. For example, newer Arduino boards,
such as UNO and Mega 2560 communicate to a PC using CDC ACM-class
device, while older boards, such as Duemilanove, use FTDI FT232
USB-to-serial converter. 3 main types of converters are
supported – CDC ACM (newer Arduinos and most modern cell phones),
FTDI FT232 (older Arduinos plus a ton of standalone converters )
and Prolific PL2303 (mainly used in USB cables for various cellphones)".
It might be a bit of a bother to port the driver over to the Micro Framework, However.