Just like that. Half my menubar space is full of icons. Sure, some are off as soon as I quit the application -the last 3- but most are the ones I see everyday. Just expand your browser window to catch all of them.
So without further ado:
Starting from the right Spotlight, Control Panel Clock [with a little hack to display both date and time], Input menu, Bluetooth status, Airport status, Volume, Keychain access, Little Snitch [in full throtle], Check off, Luna Menu, Weather Dock, Google Notifier [newer Gmail Notifier allows a priviledge escalation exploit], Adium, Gizmo and Azureus.
Some are not in Britta’s compilation as she only list menulets and not applications that can set an icon in the menubar.