PIC is a nice way to start. They've been around for a while, are cheap, easy to program and have good feature sets. Check out
this for a nice little guide on getting started with programming PICs. And see
this for good information on programming PICs using C instead of assembly. In the end you're running compiled code on a generic processor though and I find you can hit walls pretty fast when working with PIC processors. On the hardware <-> software balance you end up spending more time in software with PIC as you program around it's idiosyncrasies and optimize your code to get the performance you need.
Personally I'm an FPGA guy. Nothing quite like bypassing all that compiled code nonsense and getting down and dirty with a little Verilog and a ByteBlaster. You can get
a nice development kit from Altera (full disclosure: I work for Altera) for a hundred and fifty bucks that includes an FPGA suitable for pedal type application development, CAD software, decent A/D|D/A, debounced buttons, extensible input via an IDE type connector, an SD reader...list goes on. The only thing its missing is rotary encoders, but it's not hard to build a set of rotary encoders on an extension strip. You can use DSP development tools like Matlab and bridge to the FPGA via Altera's SOPC Builder. Lets you build up DSP algorithms in Matlab's sweet DSP building environment and then implement it directly as hardware as opposed to running it as code on a generic processor.