I like to use gmane to browse projects' mailing lists and post to them. I use a NNTP client to do this. It's great when it works, except for the few cases where posting is broken (seems to be mostly google groups lists).

On the website of my project I point users to the blog-like interface to gmane, which can be used to browse and post to a list: http://blog.gmane.org/gmane.comp.graphics.veusz.general