Mashable has a great roundup of online calendars and calendar resources that are available right now. The usual suspects are there along with some lesser-known calendars.

Of course we all know who the leader is still (at least until Yahoo releases their new Ajaxy calendar – or Brownbook 2.0 :):

I was most interested, however, in some of the ancillary services that are coming out to tie some of these services together. TwitterCal is definitely my favorite and serves to confirm my suspicion that Twitter will eventually become the command line for the Web.

On another calendar note, Brownbook is close to getting its next major release. Most of the interface has been overhauled and there are numerous new features based on feedback from our customers. We are very excited. Our baby is finally growing up.