I recently noticed this one:
http://latticesemi.com/Home/Products/DevelopmentBoardsAndKits/iCEstick.aspx
The USB stick form factor + pricing are definitely interesting.
Since you asked for xilinx ... if you can get academic pricing, this one might be interesting:
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,897&Prod=NEXYS3
Bigger fpga than that papilio, and lots more features on the board.
Or if you can get US Student pricing, this one is definitely cool:
**broken link removed**
Wish I could get it for $139, I would have bought one yesterday.