Hi Martial,
I can't say off hand without actually trying one of these devices physically and using the software and seeing the development work flows. 

You have many choices, i guess, but you'll need to take the risk and go ahead and buy one and try it out. If the software is free then it will help you get started. However, my experience is that the free software will only get you so far, and will be aimed at the lowest end of the product family. Sometime, specific productivity enhancing tools, workflows and libraries might be missing in the free versions, which will force you to eventually consider buying the paid version of the software. 

My recommendation is to go in for the new Xilinx Spartan-6 FPGA SP601 evaluation kit at USD$295. The software flows and tool support are very good. Spartan-6 FPGA SP601 Evaluation Kit.

This kit wasn't there a few weeks ago. I will also probably order this kit very soon, and migrate my integration work with the Overo with this platform. So, it will help if we share the same infrastructure. 

At the moment I am using a Xilinx ML507 Virtex-5 evaluation board, because it has an FXT chipset, which features a PowerPC core. This is useful if you want to run and operating system on the FPGA. I plan to run a light posix style run-time to manage the interface between the Overo and the FPGA. Virtex-5 FXT FPGA ML507 Evaluation Platform. This one is about USD$1195, plus you need to get the USB download probe and cable. The package for USD$1195 doesnt come with the software, neither does it support some specific features or workflows (i.e. EDK) for the FX70T processor. 

So, its better to get the full kit which costs USD$2595, which includes the full s/w (a USD$2995) cost + download probe + ML507 board, so you might end up spending a bit more initially, but you save in the long run. 

In all this, the upfront investment is a bit steep for the Virtex series. Once you have a prototype up and running, it later on just boils down to the cost of the barebones hardware for you actual system. 

You also need to be aware that you need to use a simulation software like ModelSim. So, you need to create behavioural models of your design, and test them first, and then transfer the code to the FPGA. 

So, in terms of software, you need the native development environment (Xilinx ISE, Xilinx EDK and Mentor Graphics ModelSim). After than if you want to speed up programming in VHDL, you can use a model driver development environment to automatically generate VHDL code from visual models. 

To further accelerate the development process,  you should using a C to VHDL compiler, so that for all purposes, you program in C, but generate the code in VHDL. 

Best regards,

Elvis


On Jun 27, 2009, at 3:53 PM, Martial Chateauvieux wrote:

What about this one 99$:
http://www.latticesemi.com/products/developmenthardware/cpldboards/machxostarterevaluationbo.cfm

or even 89$, USB powered, smaller:
http://www.latticesemi.com/products/developmenthardware/developmentkits/machxominidevelopmentkit.cfm

Regards
Martial