Suggestion: [code] tag

<?php 
$x = 75; 
$y = 25;
 
function addition() { 
    $GLOBALS['z'] = $GLOBALS['x'] + $GLOBALS['y']; 
}
 
addition(); 
echo $z; 
?>

<#@ output extension=".txt" #>  
<#@ assembly name="System.Xml" #>  
<#  
 System.Xml.XmlDocument configurationData = ...; // Read a data file here.  
#>  
namespace Fabrikam.<#= configurationData.SelectSingleNode("jobName").Value #>  
{  
  ... // More code here.   
}

//import
import java.awt.Color;


public class FilterExample
{
	/*
	 *pre: image != null, image.length > 1, image[0].length > 1
	 *	image is a rectangular matrix, neighberhoodSize > 0
	 *post: return a smoothed version of image
	 */
	public Color[][] smooth(Color[][] image, int neighberhoodSize)
	{	//check precondition
		assert image != null && image.length > 1 && image[0].length > 1
				&& ( neighberhoodSize > 0 ) && rectangularMatrix( image )
				: "Violation of precondition: smooth";

		Color[][] result = new Color[image.length][image[0].length];

		for(int row = 0; row < image.length; row++)
		{	for(int col = 0; col < image[0].length; col++)
			{	result[row][col] = aveOfNeighbors(image, row, col, neighberhoodSize);
			}
		}

		return result;
	}


	// helper method that determines the average color of a neighberhood
	// around a particular cell.
	private Color aveOfNeighbors(Color[][] image, int row, int col, int neighberhoodSize)
	{	int numNeighbors = 0;
		int red = 0;
		int green = 0;
		int blue = 0;

		for(int r = row - neighberhoodSize; r <= row + neighberhoodSize; r++)
		{	for(int c = col - neighberhoodSize; c <= col + neighberhoodSize; c++)
			{	if( inBounds( image, r, c ) )
				{	numNeighbors++;
					red += image[r][c].getRed();
					green += image[r][c].getGreen();
					blue += image[r][c].getBlue();
				}
			}
		}

		assert numNeighbors > 0;
		return new Color( red / numNeighbors, green / numNeighbors, blue / numNeighbors );
	}

	//helper method to determine if given coordinates are in bounds
	private boolean inBounds(Color[][] image, int row, int col)
	{	return (row >= 0) && (row <= image.length) && (col >= 0)
				&& (col < image[0].length);
	}

	//private method to ensure mat is rectangular
	private boolean rectangularMatrix( Color[][] mat )
	{	boolean isRectangular = true;
		int row = 1;
		final int COLUMNS = mat[0].length;

		while( isRectangular && row < mat.length )
		{	isRectangular = ( mat[row].length == COLUMNS );
			row++;
		}

		return isRectangular;
	}
}

 tag at the moment isn't very usable.

 tag since... it does not achieve any sort of syntax highlighting that I hoped it would. The alternative mentioned by Gav above is the closest to what I expected the [code] tag to produce, but it's rather confusing to use the [php] tag to display non-PHP code. It would be great if the [code] tag accepted some sort of input to highlight its contents, such as [code="c++"] or something similar.

Being able to parse markdown would be a great feature, I think! Markdown syntax is significantly simpler compared to BBCode, though I think the main problem would be looking for a markdown parser that would support whatever platform PC runs on nowadays. Another problem would be the whether it's actually worth all that effort since markdown essentially produces similar outputs to the BBcode-styled posts, albeit with comparatively little effort.