Here is another small modified plugin that auto-escapes your code, nicely displays line numbers and uses valid XHTML. This plugin is based off of SemCodeFix, and adds many of the features I wanted in my code plugin.

Download:
WordPress Code Escape

Directions:
Download the file and save it as a .php file.
Upload to your plugins directory.
Activate it.
You may optionally choose to add the following style information to your theme’s style.css.

.code_child {
	font-family:"Courier New", Courier, monospace;
	white-space:pre;
	width:90%;
	background-color: #F4F4F4 !important;
	overflow:auto;
	border:1px inset;
 	margin:10px;
}
ol.code_child li{
 	margin:0;
 	padding:0 !important;
 	line-height:100% !important;
 	margin-bottom: -8px;
 	margin-bottom: expression(5 +"px");
 	margin-left:  expression(35 + "px");
}