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The ARM Cortex-M1 (probably the simplest of the ARM processors) is the first ARM processor specifically designed to be implemented as a soft processor in FPGAs. It is optimized for the following FPGA types:

Actel (M1 ProASIC3 and M1 Fusion) Altera (Cyclone-II, Stratix-III) Xilinx (Spartan-3, Virtex-5)

ARM itself is making a Cortex-M1 Development Kit for Altera Cyclone III although it is a little pricey at $625 from DigiKey. You do get all of the ARM Cortex-M1 IP though, and a license to do development (plus a free royalty grant for 1000 boards for those going into production, pretty cool).

There may be some options for getting the IP by itself (perhaps they have an academic program, someone else mentioned a university program, but that was for the M0). Then you could buy a development board separately.

Here is some more information about the ARM Cortex-M1 on Altera.

Here's some information about putting a ARM Cortex-M1 on an Actel FPGA.

Meanwhile there is some interest in other versions of the ARM Cortex on FPGA; here is a paper from someone that implemented a ARM Cortex-M0 on a Xilinx FPGA.