I hope nothing is fully free. You will find the tools all the DSPs of Analog Devices (SHARC, Tiger SHARC, BLACKFIN, ADSP-21xx) are free for 90 days.
You may visit the following site for downloading
there are also free compiler for other analog device DSP and for motorola DSP56000
one should refer to the comp.dsp faq : https://www.bdti.com/faq/ on section 3 "Programmable DSP chips and their software"
I guess that they are many other that not listed, especially for general purpose processor that are used for signal procesing such as G4 from motorola or SH4 from hitachi