If you've found an interest in FPGA programming and loved the Papilio One 500K, you should definetly try the new Papilio Pro LX9!
The Papilio Pro is an open-source development platform newly upgraded on the capable Xilinx Spartan 6 LX9 FPGA.  
The newly added 64Mbit SDRam chip adds new functionality and opportunities to the Pro.
The Papilio Pro can be expanded by the use of "wings" which are stackable add-on modules, similar to Arduino shields, through the use of 48 I/O pins (don't worry, the Pro is backwards compatible with all Papilio One wings).

You can still use traditional FPGA development tools to write code for the device.
The Papilio isn't directly supported in Xilinx ISE but a script file is available on their website to load bitstreams generated by the program.

One unique feature of Papilio is that they provide a custom version of the Arduino IDE which allows to you write Arduino code and upload it to an AVR8 Soft Processor, an Arduino-compatible processor being emulated inside the FPGA!

Features:

• Fully Assembled with a Xilinx XC6SLX9 and 64Mbit SPI Flash Memory
• Easily add New Functionality with Wings that Snap onto the Board
• Two-Channel USB Connection for JTAG and Serial Communications
• Four Independent Power Rails at 5V, 3.3V, 2.5V, and 1.2V (with no detectable heat generation)
• Power Supplied by mini USB
• Input Voltage (recommended): 6.5-15V
• 48 I/O lines!

Documents:

• Schematic
• Datasheet (Spartan 6 LX9)
• Papilio Site
• Papilio-Arduino IDE
• Papilio Download Page
• Xilinx Download Page
• OpenCores Site