The ACM Conference on Object Oriented Programming, Systems, Languages, and Applications. Held once a year, this is the premier forum for anything and everything related to systems design, architecture, and implementation using OO tools, languages, and methodologies.
In 2000 it is being held at the Minneapolis Convention Center in Minneapolis, Minnesota. This year's event includes dozens of seminars, BOF sessions, panels, and other miscellany of geek culture. If you are a hacker, sysadmin, or dba responsible for building or maintaining large-scale systems, you should probably be at OOPSLA.