well, DSP has both traditional effects like lowpass and highpasss filters, as well as equalizers.
DSPs allow for more then just these simple linear effects though. on some units you can add echo/reverb and other effects. room simulation and sometimes even simulating a tube amp. generally these effects are overdone.
also there is the popular bass cube, fairly popular DSP.
It my goal to one day put a mac mini in my car and use it for DSP.