The original samsung series 9 is a sandybridge "ultrabook" from 2011 that can take 16GB of ram. While technically before ultrabooks were first released, it has a similar profile to the air. It was also released before 8GB dimm modules were available, but while never being "supported", they work just fine.

I haven't seen an ultrabook I'd prefer over it, especially when I rule out ones that use a tapered design.

My macbook pro isn't that much thicker than an air.. though I wound up getting the 15" retina because I needed 16gb without waiting a few weeks for it... tried an 8gb/13" retina model, and returned it, needed the extra ram.