zvents is very pale-blue-and-orange-with-white-space Web 2.0, similar to Eventful: I'm seeing this look a lot at the moment. Unlike , it only covers the Bay area. You can search by events, venues, tags, groups or people, and when you get the results you can switch the list to a map view or a calendar view. With a lot of results the map and main calendar view show you the number of results rather than the individual events, but you can get a 1 day, 3 day, 7 day and 30 day view as well. Here it's the guided tours that dominate rather than the bookstore events, but when you get down to individual events they're very well presented with maps, times, repeat events, similar events, other events at the same venue... More useful details than Eventful.
AllConferences has a hierarchical drill-down of categories and an advanced search, though you can only search by one condition and picking March 2006 without a date produces events from June 2004 as well. There are conferences going back to 2001 and those are what you see when you search by City; the general search box does a better job. Look here for commercial and academic conferences.
These sites tend to be better for finding a specific event on a specific day than browsing through the possibilities for a longer period of time. For that, I want to be able to start with a large pool of results and filter them. The best filtered view of search results I can think of - and it has deficiencies still - is the hotel map view in Expedia; you can zoom in on the map to refine the list of hotels, or remove hotels from the list to clear them from the map view. I'd like the same for events; let me zoom in to an area, or a category of events, or a smaller date range, or to a time range across several days (what's on every evening next week?). Let me remove all the sports events and everything that's recurring rather than a one-off and trim down from any day in March to just these 9 days. It's all about underlying hierarchies of logical units: know that a week is a logical unit of a month, know that Kirkland is within the greater Seattle area. Some of this you can do with a folksonomy, but a categorised hierarchy is going to help for geography, discrete units (today/tomorrow/this week/next week/this month/next month/this year) and distinguishing between broad tags (music) and specific tags (baroque). Organic tagging can define a problem space, but it doesn't structure it well.
Do we have these kind of detailed schemas for describing not just the obvious properties of events (date, time, venue, organiser etc) but also the range of values so we can build the filters?