Gnuplot

Basic x / y plot of data from a file in the form:

x1 y1
x2 y2
x3 y3

set ytic auto
set xtic auto
set title "iCal Server Queue Depth / Latency"
set xlabel "Queue Depth"
set ylabel "Latency"
plot "ical-queues.tx t" using 1:1 title "Queue Depth" with lines
plot "ical-queues.txt" using 1:2 title "Latency" with lines