Although you can log data from an Arduino-based system to a microSD card (possible with our EtherTen and EtherMega boards) - when the volume of data being logged is large, or you need real-time analysis a new piece of software called MegunoLink may be of interest. It has six primary functions, including plotting data from the serial line to a graph:
as well as logging data to a text file, interfacing between Atmel AVRStudio as an alternative to the Arduino IDE, a graphical interface for avr-dude, an advanced serial port monitor, and a clever interactive serial protocol simulator. MegunoLink is a simple, yet useful piece of software that is documented well and free to download. If you find it useful a donation should be made to the supplier. For more information, visit the MegunoLink product pages.