I'll start. Believe it or not, I still use Outlook Express, but with what must be over 100 custom mail filters sorting messages into folders. I use server-side anti-spam and AV combined with a client-side Bayesian spam filter and client AV app. (Raw unfiltered, I receive roughly over a thousand messages every 24-48 hours.) I also access mail via a web app, mainly for training the server-side filters and for access to a slick Ajax-style calendar and document sharing program we use. I've considered going to all server-stored mail and relying on the web client, but haven't yet made the leap. All told, I use four accounts and two more aliases to make incoming mail easier to sort and prioritize.
What do you use, and how important is e-mail to you now? Could e-mail be made more useful with widespread adoption of protocols to authenticate senders? Discuss.