Orbiter is a visualisation of satellite orbits around earth. You can play with the 5 Kepler parameters a, e, i, pa, raan (semi-major axis, eccentricy, inclination, argument of perigee, right ascension of ascending node) and see how the corresponding orbit looks like.
You may try it out (Linux x86, Mac universal, Windows XP) via Orbiter webstart or multi-platform Orbiter installer. Arrows keys and PgUp/PgDown for camera, Return for accepting text field values, "play" toggle buttons for parameter animation. OpenGL and JRE 1.5 required.
My thanks go to the following library projects: JOGL (OpenGL for Java), Orekit (orbit model), Apache commons-math (general mathematics), JGoodies (forms for layout, looks for Look & Feel), Eclipse (rich client platform), SwtForms (layout for SWT), and IzPack (installer).