If Outlook's attention-grabbing desktop pings are the main reason you stick with it, Google Calendar might surprise you. After enabling a Labs feature and a Chrome setting, you can get similar notifications so you don't miss that meeting or lunch outing.
The How-To Geek's home away from Lifehacker has a how-to write-up from the man himself, a previously devoted Outlook user who's now considering a Chrome/Calendar combination to keep on top of what's happening. The drawback is that you have to keep Chrome running to keep the notifications coming, of course, and you might not like having to click on each notifier to make it go away. Then again, that persistence might be just what you need.