What monitor as second monitor for iMac 24"?

I recently bought the iMac 24", and I want to try out a second monitor when editing in Final Cut Pro and Photoshop. I do not want a second monitor as a monitor that just take up space, so I considered an iPad a better choice.. How will this work? How is the screen as a monitor (I know, it depends on what iPad). I don't think I will use the iPad as the grading monitor, but for tools, functions, Finder, option bar, etc. Simply want to extend size of the 24". Any suggestions?