Free Agent (32-bit) is an excellent Usenet newsgroup reader.
It has a superb user interface and it works both online and offline. Features include: the ability to view images and binary attachments; an intelligent header and article database; multi-level article threading using both the subject and article ID so that you always know exactly what an article is in response to; quoted text highlighting; a "dip into it" feature for checking out new newsgroups by viewing only recent articles; customizable signatures; internal multitasking so that you can do many online tasks at once; and much more.