Here is the MySQL function to use to get the current datetime as ISO 8601 format as asked in DarwinCore:

DATE_FORMAT(NOW(),'%Y-%m-%dT%TZ')

DATE_FORMAT() is obviously a function for formatting date and time, and we are using here %Y for four-digit year, %m for two-digits month, %d for two-digits day and %T for 24-hour time (hh:mm:ss). NOW() gives the current datetime.

And then you get a nice figure like this one:

2009-06-10T07:43:12Z

Note that the same result can be achieved with:
CONCAT(CURDATE(),'T',CURTIME(),'Z')

Where CONCAT() is used for concatenating strings, and CURDATE() and CURTIME() give respectively the current date and the current time.

UPDATE: There is now a page for getting the current datetime in different formats. Check the page here: Get the current date in different formats in MySQL.