You can use Excel 2011 for Mac by displaying spreadsheets side by side.
- Open any spreadsheets that you want to view side by side
- Then go to "Layout" tab
- Look under "Window" group and select "Arrange"
- In there, you can display spreadsheets vertically or cascade the windows
- Select "Arrange Windows ... " for the full range of options
- Choose the way you want your windows to display, and select OK to apply your change