Well, for starters if your ISP finds out you are doing this, they will more than likely shut you off for good unless you pay like $400 a month for your HSI.
You'll want to at least have port 80 and 8080 open for basic HTML pages. Anything that uses MySQL or the likes will need more ports open like 3306 and 8888 (or that's at least how my servers are setup)
$400? Ack! My cable provider charges $69.00 for a tier of service called SOHO (small office/home office) that gives you a static IP and lets you host whatever the heck you want.