According to this blog post from the Young and Catholic blog, the location for World Youth Day 2008 is “semi-official”: Sydney, Australia. According to the blog post:

The “official”, official announcement won’t be made until the end of the Mass and activities taking place at Marienfeld on August 21.

For World Youth Day 2005 coverage, I suggest you check out the Catholic Insider podcast, which is a member of Disciples with Microphones.