Assuming you are a Haskeller, you can get a simply x-y plot up very quickly with the gnuplot interface module. This is useful for getting a rough graphical view of some function. Simply...
1. install Gnuplot (through your package manager)
2. cabal install gnuplot
3. use ghci:
GHCi, version 7.4.1: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ...