KWizCom has a neat calendar rollup webpart that I figured is worth showcasing. It can rollup multiple calendars across multiple sites, into one central calendar. Also, it can access exchange calendars as well, making it a pretty powerful tool. That and it is only $399 which makes it practically free!
Screen shot (notice color coding, signifying the different calendar sources):
[this post was cross-posted from http://philwicklund.com]