It depends on what you need - if you want binaries, then I've been using Newshosting for a few years and would recommend them - approx �9 per month (depending on exchange rate) for unlimited downloads and 100 days retention.
I've never found any decent free ones. I've also found that newsgroups provided by ISPs are generally rubbish for binaries, but ok for text-only discussion groups.
In general, if you want binaries and high rates of completeness, then pay servers are the way to go.