Opp's you may want it to appear solid by adding a disk to the end!
IntPtr i = new IntPtr();
i = gl.NewQuadric();
gl.QuadricNormals(i, OpenGL.GL_SMOOTH);
gl.Cylinder(i, 2, 0, 8, 120, 16);
gl.Disk(i, 2, 0, 120, 1);