There are websites that turn email into a game; it shocks me how good a motivator this can be (I guess part of me IS still a child).

My recent favorite is http://emailga.me (NB: gmail only)

The combination of timer count-down, smileys and 'rounds' is rather clever. And more importantly: effective.

This doesn't help with the paralysis induced by longer emails that deserve an equally thoughtful (read: time-consuming) reply.

For those I pick up the phone. It's retro, but saves time in many cases.