Not so long ago, this article:
"Google Labs and Google App Engine URLs"
http://www.google.com/support/a/bin/answer.py?answer=91080
described the following set of four ips for use in DNS A records:
216.239.32.21
216.239.34.21
216.239.36.21
216.239.38.21
That information has been removed from the article and I can no longer
find it anywhere. A while back I set up one of my domains using all
four ips, and now I'm setting up some others and wonder if the advice
is still good or has it been deprecated?
Doc
PS: That article has been (I think) widely referenced in this group.
For example:
http://groups.google.com/group/google-appengine/msg/2717ea51fc36070b