Mad Props!

Here's a revised version of my "data bars in a DataGridView" code. This one introduces a small margin, and reworks the gradient fill slightly. It also makes the maximum value in the column represent 100% of the width of the data bar, so it's more like Excel 12's version.

First, the code (obviously dataBarColor is a private variable representing the colour of the data bar):

private void dataGridView1_CellPainting(object sender, 
    DataGridViewCellPaintingEventArgs e)
{ 
    DataGridView dgv = sender as DataGridView; 
    if (dgv.DataSource == null) return; 

    if (e.ColumnIndex == 1 && e.RowIndex >= 0)
    {
        if ((e.State & DataGridViewElementStates.Selected) 
            != DataGridViewElementStates.Selected)
        {
            Rectangle rect = e.CellBounds;
            e.PaintBackground(rect, true);
            rect.Offset(-1, 2);
            rect.Height -= 5;

            double value;
            double max = 0;
            for (int i = 0; i < dgv.RowCount; i++)
            {
                value = (double)dgv[e.ColumnIndex, i].Value;
                if (value > max) max = value;
            }

            rect.Width = max == 0 ? 0 : (int)((double)e.Value * rect.Width / max + 1);

            if (rect.Width > 0)
            {
                using (LinearGradientBrush lgb = new LinearGradientBrush(rect, 
                    dataBarColor, e.CellStyle.BackColor, 0.0))
                { 
                    Blend blend = new Blend(); 
                    blend.Factors = new float[] { 0, 0, 0.8f }; 
                    blend.Positions = new float[] { 0.0f, 0.3f, 1.0f }; 
                    lgb.Blend = blend; 
                    rect.Offset(1, 0); 
                    rect.Width -= 2; 
                    e.Graphics.FillRectangle(lgb, rect); 
                } 
            } 

            e.PaintContent(e.CellBounds); 
            e.Handled = true; 
        } 
    } 
} 

And a screenshot: