Be sure to look at this logger http://arduino.cc/forum/index.php/topic,153598.0.html
It logs multiple analog pins to a text file.
It can log two or three analog pins on a Due at 1000 Hz and all Due analog pins at about 500 Hz.
All 16 Mega analog pins can be logged at 100 Hz.
Here is an example Mega file with all 16 pins read every 10 ms. The pins are floating so the values trend to zero due to charging the ADC sample and hold cap.