[plug] OT Any ISPs allow intelligent Spam filtering?

[Daniel]

Hi Plug,
I'm sorry my understanding is still badly lacking on this spam filtering 
business.
I considered forwarding my mail to a free service with a good spam filter 
but I couldn't find one that was above the basic level.
I've looked at a few spam filtering mechanisms, but I am reluctant to have 
a permanent connection just to filter spam - can anyone tell me of an isp 
that offers a comprehensive spam filtering service (like those below)?

I have looked at the following [on the off chance I can't find an isp] to 
try to learn more, but I think they require abilities and services many 
isps might be reluctant to give.

Any ideas?

Spambouncer
http://www.devsite.org/internet/noframes.shtml
seems very thorough and to have quite a following ... Procmail focused.

Active Spam Killer (ASK)
http://www.paganini.net/ask/
likewise seems good. Procmail focused.

Tagged Message Delivery Agent (TMDA)
http://software.libertine.org/tmda/index.html
imho - wants to make a new e-mail address that is open for a short period 
of time to receive replies.
Overkill for the trouble?  Works more broadly than just Procmail.

TIA
Regards,
Daniel