Thought #1
I would like a Word Count Filter; where I can filter emails that have more than 5 "<!-" in the body.

Thought #2
I am also a software developer and would love to be able to code my own rules, or even help you guys out if there was a Rule Plugin feature...

Look at http://www.workgroupmail.com/ This is an email server that allows custom Plug-In's (written in VB or C) to scan and filter email. You can then provide a Plug-In download section.

1) It's fairly easy to write a filter that will count the number of "<!-" - but you'll probably want to expand that to "<!" (since most spammers don't seem to use the accepted comment syntax) and increase the number of occurrences, if you don't use some other limit, or you will probably get falsing. I use this expression:

((<![\w\s,\.\-]+>)([\w\s,\.\-]){1,20}){3}

and I'm working on some to catch the fake HTML tags.