I created a patch that enables a box floating on the left of the overview page showing the latest value of the item one is hovering..
(here's a screenshot: http://www.zabbix.com/forum/attachment.php?attachmentid=1073&d=1197045707)

I was asked by richlv to ask you for inclusion.

http://www.zabbix.com/forum/attachment.php?attachmentid=1075&d=1197045883

As far as I'm concerned, this work is public domain, I don't claim any copyright.