I am really wanting to upgrade to the 5D Mark II....Is the 24-105mm a great companion for this? Will the 24-105mm serve me well for landscapes?
The 24-105L is a great all around lens for the 5D full frame bodies. It "may" be wide enough for your landscape shooting on the 5D2, so I would hold of on purchasing any ultra-wide angle lens if you are serious about upgrading to full frame in the next couple of months.
The Canon EFS 10-22mm is an excellent UWA lens, and compares very well on a crop body versus the 17-40L on a full frame. However, the 10-22mm will not work on a full frame body without modification -- hence why you should hold off purchasing if you are that close to buying into a full frame body.