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Everything ARM and LPC
By Anigam
Hi all, ... pen_source - Yoggie released their Linux ARM-based (XScale) hardware platform with full Linux shell access, along with SDK and BSP source codes. Meaning, you get the full PXA270 @ 520MHz, 128MB SDRAM, 128MB NAND Flash, USB product, platform and everything for $49 (!!!)

As far as I know this is BY FAR the cheapest, strongest, smallest platform available… :-)
The device already comes with firewall application running, with GUI and everything. Beyond the fact you can play around and research what's going on inside or even implement new features – You can actually use this as a platform to develop anything you want from scratch.