Alexander Wirt was so kind to upload the latest icinga (1.2) release to unstable. This will be the next candidate for lenny-backports-sloppy.
If you can't wait, just grab the package from http://ftp.cyconet.org/debian/archive/bpo/icinga/1.2-1~bpo50+1/.
If you are using nagstamon and thinking about upgrading to icinga 1.2, I backported a working version from subversion r151, which you can grab from http://ftp.cyconet.org/debian/archive/bpo/nagstamon/0.9.4r151.1~bpo50+1/.
P.S. If you like nagios and/or icinga related software, there is a Nagios Maintainers Group and we would like to invite you, if you want to improve or extend the nagios/icinga ecosystem in Debian.