Digital signal controller with GNU toolchain?
You don't mention what sort of power you need, but the AD Blackfin and TI OMAP devices both are supported by open source toolchains (gcc etc).  For OMAP, look at OpenEmbedded @ www.openembedded.org/wiki/Main_Page , for Blackfin have a look at ucLinux @ www.uclinux.org/ .

Even if they seem over the top for capability (up to around 1GHz ARM + DSP), they are small and power efficient, e.g. see Gumstix Overo @ www.gumstix.com/store/index.php?cPath=33 for a range of OMAP boards and a good developer community @ gumstix.org ).

OMAP is also used on the Beagleboard, which is a great place to get started.

(Apologies, first post to electronics.stackexchange so limited to 2 hyperlinks, hence the untidiness above!)