HA options

Hey Guys.

It's been a while since I looked into this and it seems like new
options have cropped up for postgres HA and scalability.   Is there a
consensus on the "best" way to achieve HA. My primary concern is HA
but of course any scalability gains would be more than welcome.  All
the servers will be virtual on either rackspace or amazon so that's
possibly a complication.

The options I am looking at are.

http://postgres-xc.sourceforge.net/  Is this production ready?
http://www.repmgr.org/
http://www.pgpool.net/mediawiki/index.php/Main_Page
http://www.continuent.com/downloads/documentation
http://www.drbd.org/ ??
Built in hot standby and hand rolled scripts.

are there others I should look at?

Thanks