Surfing, I´ve found a good free software: Kst http://kst.kde.org/ (Windows and Linux)
" Kst is the fastest real-time large-dataset viewing and plotting tool available and has basic data analysis functionality."
In windows, with Realterm and Kst, you achieve a quick & easy method to plot data form your Arduino in "real-time".
I´ve write a mini how-to in spanish (sorry!! but google translator works quite good) => http://real2electronics.blogspot.com/2009/11/graficar-con-kst.html