The best web-based calendar is kiko. The format is simple and clean and it’s easy to work. It also allows you to invite friends and they can look over what’s you want them to view as far as your calendar is concerned.
The other calendar is called calendarhub. Once again, simple is good and it allows you to do all of the things that kiko does, but for some reason I like the kiko interface better. Looking at it objectively, calendarhub allows you to do more, like publish your calendar to your blog and allows you to look for local events in the area.
Both are good strong calendar systems and I recommend them both. Also, it’s free, and there’s one thing I’ve learned since starting this stuff is that there’s no real reason to pay for anything because you can get it free (Miranda will strongly disagree with me, but its true).