Servers

Before you go out and pay for any kind of newsgroup access (adult or otherwise) please read the promotional materials of your ISP. Why? Because virtually all ISPs provide newsgroup servers for their subscribers. These newsgroup servers are free to subscribers and they are generally NOT censored. They may not offer all of the newsgroups in which you are interested, but if you don't have specific groups in mind these may be just the ticket.

The primary advantages of the ISP newsgroup server, in general, are:

Comes free with service
Usually uncensored
Usually unlimited bandwidth
Contains newsgroups related to service (a good argument for using the ISP newsgroup servers in addition to paid ones if you do go elsewhere).

Some disadvantages include:

Not their primary business (just an add-on), so generally not well maintained
Often does not carry some of the larger binary newsgroups
May be censored (haven't found one that's censored yet, but you never know).
If you change ISPs you've lost your feed to the newsgroup servers (but they are easy to find so who cares?)

Some of the newsgroup servers that I've found while surfing the net are listed below.

Terranews: This is a service which offers free and paid access to newsgroups. They claim to allow access to all newsgroups, and the spot checking that I did supports this claim. You simply sign up for an account (and a free account does require a credit card to validate age) and define the news server in your newsgroup client. It took me less than 5 minutes.
Google: Believe it or not, Google now offers access to newsgroup archive searches. The advantage to this feature is that it's free and easy. The disadvantage is Google does not support binary files, and they do not seem to keep the archived messages for more than a few months.
Newsfeeds: Paid newsgroup service which seems a bit on the expensive side to me. Their unlimited bandwidth plan is about $40 a month. They host binary newsgroups (in fact they claim this is their specialty) and at that price they had better be good.
Newsguy: Another paid newsgroup service which is not very expensive. At the basic rate you can download 10mb per day.