Web Based

Mailarchive.ca - Read-only access to a collection of newsgroups, some of them being archived since 2001.
http://www.mailarchive.ca/

Microsoft Newsgroups - Free access to many newsgroups focused on Microsoft and their products. Requires Internet Explorer.
http://www.microsoft.com/communities/newsgroups/default.mspx

Dbforums - Provides access to database-related groups. Requires free registration for some features.
http://www.dbforums.com/forumdisplay.php?forumid=23

PictureView - Provides Web-based access to binary newsgroups including pictures and videos. A free demo is available.
http://wwv.pictureview.com/

1-script.com: Web Developer's Archive - Archives messages in the Usenet groups that are relevant to web development, design and programming.
http://www.1-script.com/forums/

Midtown Computer Systems - Provides access to IT certifications and software related newsgroups. Posting and searching require free registration.
http://www.mcse.ms/

Nonsolonews - Free web access to a large number of newsgroups. Posting requires free registration.
http://www.nonsolonews.net/

Usenet Replayer Wap Gateway - Read-only access to Usenet via a Wap enabled mobile phone or a Wap emulator such as wmlbrowser add-on for Firefox. A usual web browser like Internet Explorer won't work. The Wap (Wireless Access Protocol) is also known as Mobile Web in North America.
http://wap.usenet-replayer.com/

Synchro.net - A read-only Gopher gateway to some newsgroups focusing on programming and BBS systems.
gopher://vert.synchro.net/1grp:usenet

Techie Groups - Provides a web service where users can read and post from and to computer related usenet groups. Posting requires free registration.
http://www.techiegroups.com/

News-reader.org - Free anonymous access to text-only groups. Provides search and posting capabilities.
http://news-reader.org/

Recgroups - Free community-oriented site focusing on select rec.* and alt.* newsgroups. Posting requires free registration.
http://www.recgroups.com/

Derkeiler.com: Usenet Source - Real-time updated, read-only archive of newsgroups. Allows to save posts in PDF format.
http://newsgroups.derkeiler.com/

Usenet.com.au - A free service that archives popular Australian newsgroups. Also includes a section on Usenet terms and netiquette and a truncated URL service.
http://www.usenet.com.au/

Jeremino.autounix.net - Based on the open source NewsPortal software, provides free access to many hierarchies, including some binary newsgroups. Free registration required.
http://jeremino.autounix.com/newsportal/

Unix Admin Talk - Free read and write access to Unix related groups. Doesn't support threaded view.
http://www.unixadmintalk.com/

Low Price - Free access to newsgroups in the ott.* hierarchy (Ottawa, Canada).
http://www.lowprice.ca/

NewsKabob - Newsgroup plugin for webmasters, serves as a web-Usenet gateway. Can be used as a service with no additional hardware or bandwidth requirements. Monthly pricing depends on the number of allowed users.
http://www.newskabob.com/

Usenet -forums.com - Read-only access to GNU/Linux, programming and some other technical newsgroups.
http://www.usenet-forums.com/

Myreader - Free access to text newsgroups in the uk.* hierarchy. Posting requires free registration.
http://www.myreader.co.uk/

Adras - Free read-only access to newsgroups focusing on information technology topics.
http://www.adras.com/