Using GDI+ encapsulated in a class to display a primitive line chart. The class features an array list to hold a dynamic number of chart points and utilizes transforms to simplify the plotting of worldview data points. Enhancements would add color options, multiple lines, other chart types, and printing.

<%@ Page Language="C#" %>
<%@ Import Namespace="System" %>
<%@ Import Namespace="System.Drawing" %>
<%@ Import Namespace="System.Drawing.Drawing2D" %>
<%@ Import Namespace="System.Drawing.Imaging" %>
<script language="C#" runat="server">
class LineChart
{

    public Bitmap b;
    public string Title="Default Title";
    public ArrayList chartValues = new ArrayList();
    public float Xorigin=0, Yorigin=0;
    public float ScaleX, ScaleY;
    public float Xdivs=2, Ydivs=2;
    private int Width, Height;
    private Graphics g;
    private Page p;
    struct datapoint
    {
        public float x;
        public float y;
        public bool valid;
    }

     public LineChart(int myWidth, int myHeight, Page myPage)

    {
        Width = myWidth; Height = myHeight;
        ScaleX = myWidth; ScaleY = myHeight;
        b = new Bitmap(myWidth, myHeight);
        g = Graphics.FromImage(b);
        p = myPage;
    }
    public void AddValue(int x, int y)
    {
        datapoint myPoint;
        myPoint.x=x;
        myPoint.y=y;
        myPoint.valid=true;
        chartValues.Add(myPoint);
    }
    public void Draw()
    {
        int i;

        float x, y, x0, y0;
        string myLabel;
        Pen blackPen = new Pen(Color.Black,1);
        Brush blackBrush = new SolidBrush(Color.Black);
        Font axesFont = new Font("arial",10);
        p.Response.ContentType="image/jpeg";
        g.FillRectangle(new
        SolidBrush(Color.LightYellow),0,0,Width,Height);
        int ChartInset = 50;
        int ChartWidth = Width-(2*ChartInset);
        int ChartHeight = Height-(2*ChartInset);
        g.DrawRectangle(new Pen(Color.Black,1),ChartInset,ChartInset,ChartWidth,ChartHeight);
    g.DrawString(Title, new Font("arial",14), blackBrush, Width/3, 10);
        for(i=0; i<=Xdivs; i++)
        {
            x=ChartInset+(i*ChartWidth)/Xdivs;
            y=ChartHeight+ChartInset;
            myLabel = (Xorigin + (ScaleX*i/Xdivs)).ToString();
            g.DrawString(myLabel, axesFont, blackBrush, x-4, y+10);
            g.DrawLine(blackPen, x, y+2, x, y-2);
        }
        for(i=0; i<=Ydivs; i++)
        {
            x=ChartInset;
            y=ChartHeight+ChartInset-(i*ChartHeight/Ydivs);
            myLabel = (Yorigin + (ScaleY*i/Ydivs)).ToString();
            g.DrawString(myLabel, axesFont, blackBrush, 5, y-6);
            g.DrawLine(blackPen, x+2, y, x-2, y);
        }
         g.RotateTransform(180);
        g.TranslateTransform(0,-Height);
        g.TranslateTransform(-ChartInset,ChartInset);
        g.ScaleTransform(-1, 1);
        datapoint prevPoint = new datapoint();
        prevPoint.valid=false;
        foreach(datapoint myPoint in chartValues)
        {
            if(prevPoint.valid==true)
            {
                x0=ChartWidth*(prevPoint.x-Xorigin)/ScaleX;
                y0=ChartHeight*(prevPoint.y-Yorigin)/ScaleY;
                x=ChartWidth*(myPoint.x-Xorigin)/ScaleX;
                y=ChartHeight*(myPoint.y-Yorigin)/ScaleY;
                g.DrawLine(blackPen,x0,y0,x,y);
                g.FillEllipse(blackBrush,x0-2,y0-2,4,4);
                g.FillEllipse(blackBrush,x-2,y-2,4,4);
            }
            prevPoint = myPoint;
        }

         b.Save(p.Response.OutputStream, ImageFormat.Jpeg);
    }

     ~LineChart()
    {

        g.Dispose();
        b.Dispose();
    }
}
void Page_Load(Object sender, EventArgs e)
{
    LineChart c = new LineChart(640, 480, Page);
    c.Title="My Line Chart";
    c.Xorigin=0; c.ScaleX=500; c.Xdivs=5;
    c.Yorigin=0; c.ScaleY=1000; c.Ydivs=5;
    c.AddValue(50,50);
    c.AddValue(100,100);
    c.AddValue(200,150);
    c.AddValue(450,450);
    c.Draw();
}
</script>