>>Microsoft Outlook Express will let you sort by threads.
>
>You mean, it will GROUP by threads, right? That is important (I've never turned that feature off!), but I really need to track threads I've contributed to, and threads I've marked as interesting.
>
>Anything that will fit the bill?

MicroPlanet Gravity works well: it's threaded, it allows you to filter on articles which are in reply to yours, and lets you mark threads to Watch.

http://www.microplanet.com/