New, I don't think there is an alternative, though nothing wrong with the 2011 Mustang GT, just don't see it as a competitor.
Used there are some options, but you end up talking maintenance costs out of Z range - I think a used Cayman, a used NSX, a used Corvette are options to consider. Oh, and I guess a Lotuz Exigencies could fit, though I don't think I'd want one as a daily driver, and I have been fairly hardcore before
Since I have a mid-engine bias, and auto, I considered the Cayman S PDK or another NSX before compromising mid-engine for performance and amenities and got the 370Z. I think it is unbeatable in it's price range.