The following are US centred and contain a lot of junk, download only headers to be sure to save bandwidth. The alt.politics group contains many, many subgroups. As these are changing almost weekly they are not listed in their entirity here. These are the 'main' groups of interest. The content of the UK based newsgroups is generally very good.
Discussion is often intensive and threads can be very long and detailed.
The busiest is the .misc group, but the subject matter often overlaps with the others. Many of the groups have many subgroups. These are constantly being added. This list is partially obtained from Lobster 31 suppliment complied by Jane Affleck.