Just found this. Thought I'd share. Looks very useful.
http://code.google.com/p/the-bus-pirate/
Also found on ebay:
http://cgi.ebay.co.uk/USB-Bus-Pirate-Universal-Interface-v3-I2C-SPI-JTAG_W0QQitemZ120486083976QQcmdZViewItemQQptZLH_DefaultDomain_3?hash=item1c0d87bd88
http://code.google.com/p/the-bus-pirate/
Also found on ebay:
http://cgi.ebay.co.uk/USB-Bus-Pirate-Universal-Interface-v3-I2C-SPI-JTAG_W0QQitemZ120486083976QQcmdZViewItemQQptZLH_DefaultDomain_3?hash=item1c0d87bd88