I'm in the same boat as the OP, currently have a 2012 i7/8GB and love it. The MBA is just the most complete package out of all the ultraportables and its tough to find others that stack up. I'm looking forward to seeing what the new MBA brings at WWDC.
That said, the closest competitors to the 11" MBA (IMO) are:
Disclaimer: Ignoring OS differences, and placing higher value on DisplayPort for high resolution desktop monitor usage.
Surface Pro - very different, but has close to equivalent computing power. No 8GB RAM option, slightly smaller screen (but higher resolution). Does have some narrow usage scenario pros (tablet use, stylus).
Toshiba Kirabook - screen on par with rMBP 13" but bigger form factor, decent looks. No DisplayPort, new product so I'd be hesitant to try it out.
Asus UX21A Prime - Good aesthetics, no 8GB RAM option, no DisplayPort. 1080p. Has been around for a few iterations so should have some polish to it.
Dell XPS 13 - Seems to be best of the bunch. 13" screen in form factor slightly larger than 11" MBA, has equivalent processor options and 8GB RAM, DisplayPort, 1080p, good aesthetics.
To the OP: the XPS 13 has matured into what appears to be the most complete competitor to the MBA, and with Windows 8.1 + Haswell it will be very good. It still remains to be seen what 10.9 and the 2013 MBA will bring, but the OS-agnostic user searching for a new computer has 2 very good options to choose from.