Update Manager Indicator is an appindicator that brings back the old Update Manager behavior (an orange icon is displayed on the panel when updates are available) with some extra features like displaying a list of updates in a submenu, option to refresh the repositories or display NotifyOSD notifications.
In its preferences you'll also find an option to disable the Update Manager auto-popup.
Update Manager Indicator source code is available @ Launchpad, but to make it easier to install, I've uploaded it to the main WebUpd8 PPA.
Add the WebUpd8 PPA and install Update Manager Indicator using the commands below (package available for Ubuntu 11.04 and 11.10):
sudo add-apt-repository ppa:nilarimogard/webupd8 sudo apt-get update sudo apt-get install indicator-updatemanager
Once installed, search for "Update Manager Indicator" in Dash / main menu.
To launch Update Manager Indicator on startup, open the Startup Applications dialog, click "Add", enter "Update Manager Indicator" under "Name" and "/usr/bin/UpdateIndicator" under command.
Report any bugs you may find @ Launchpad.