hardware choices which i think will do what you want:
The Digitech Jamman stereo will do that,you can store backing tracks,your own loops etc.and there is a software called jammanager to make workflow easy
it has,reverse,undo/redo and something like 99 slots to store wqhich you can easily scroll through,i have it and thats plus its size is what was attractive for me
The new RC-300 is very good though,you can also store loops or back.tracks and it has 3 independent tracks which you can be of any length, stop and start independently undo,redo,reverse and pre or post fx
you can also use it in "next track mode" to change between arrangments parts like with the echoplex "next loop" function
and
offcourse mic input,instr input,main outs and sub outs for monitor mix plus ann assignable exp pedal for independent volume control,fx etx. is big for a pedalboard though!
cheers
Luis
http://www.myspace.com/luisangulocom