When I had comcast I think they shut down their own servers and instead offered 1GB accouts to giganews. A google search for comcast usenet says they shut off their servers.
http://www.news.astraweb.com/ is what I've been using for about 4 or 5 years.
$25 for 180GB isn't too bad. The accounts don't expire, I've left my account idle for over a year and come back and used my remaining credit. I've never done the monthly plan. If you use the SSL servers I don't think your ISP can see what you're getting.
For a client I use altbinz
http://www.altbinz.net/index.php
For nzb's, I use
http://nzbs.org/ (free registration). Definitely the best site I've seen for nzb's. Also
http://www.newzleech.com/ is pretty good.