I am a little obsessed with online productivity tools! I love my iGoogle page the most. I like iGoogle because I see it every time I go to try and google something (which is very often.)
I also love del.icio.us because I work on several computers throughout the day and I always know that I always have access to my bookmarks.
In the past I have used google calendars quite a bit, but I have since used it less because I feel like the outlook calendar is better for school events (since so many of our meetings are set up in this manner.) Last year I figured out how to link my outlook calendar to automatically update my google calendar. However, my machine was cloned and I haven't had time to re-do that program. For me...opening my web-email is just as easy.
I also experimented with Remember the Milk last year and found that outlook task lists worked better FOR ME.