8601 provides a variety of interesting format variations. I routinely wish to use, but can never remember, the following:
$ TZ=UTC date +%Y-%m-%dT%H:%M:%SZ 2009-10-29T04:10:09Z $ date +%Y-%m-%dT%H:%M:%S%Z 2009-10-29T12:10:43SGT $
Recorded here for easy reference next time.