For the last couple of months I've become increasingly addicted to the Netvibes service. If you haven't experienced it yet, I highly recommend the site.
Netvibes is one of the best designed, most user-friendly and intuitive Web 2.0 sites I have seen. It's so intuituve, in fact, that there's no welcome screen or instructions - it just pops you right into a fully customizable home page. On the page you can read RSS feeds from your favorite blogs, check email from numerous accounts, keep track of your MySpace page - pretty much anything that requires you to keep up with new information can be tracked from your Netvibes page. I find myself checking my Netvibes page throughout the day.
While other companies like Yahoo and Google offer similar home page functionality, I prefer Netvibes for its ultra-clean interface and easy customization. Try moving around a module on your Netvibes page by dragging it across the screen and see how intuitive it feels - this is a great use of Ajax.
There's no advertising and I'm not sure I see what their business model is yet, though I have some ideas of what they might do down the road. Netvibes has been growing rapidly via word of mouth and it's easy to see why.