GMail's new Priority Inbox feature is kind of neat. Despite the cheesy animated explanation, the idea is nice and solid, and the implementation pretty good too. Basically, it extends the built-in spam filter a level further to determine which of your incoming emails are the most important and which can wait for later (but aren't spam).
I was doing a similar thing with my work email a few years ago via Thunderbird's built-in spam filtering, and it was extremely effective. I look forward to the same results in my GMail account, but first I might have to disable a few of my filters - until now I was using them to hold back unimportant emails. Now if only Outlook could catch up and include features that are in all the other email clients.
Mokalus of Borg
PS - I say "all the others", but I'm only thinking of GMail and Thunderbird.
PPS - Though I'm sure there are more that beat Outlook at certain tasks.