You won't see any "new" ultrabooks before June/July given that many manufacturers (including Apple) are waiting for the release of the Intel Ivy Bridge ULV chips which aren't released yet. It would be better to wait until then to consider the options since we don't have much details regarding upcoming ultrabooks yet.
As for the current options with Sandy Bridge, I think the best ultrabooks are the Asus Zenbook followed by the Samsung Series 9, but nothing beats the current MacBook Air.
The Zenbook is slightly cheaper and has similar specs and form factor as a MacBook Air, but lacks a backlit keyboard, has worse viewing angles, and its trackpad (and Windows drivers for it) isn't nearly as good as the MacBook Air's.
The Series 9 is slightly more expensive than a MacBook Air, does have a backlit keyboard, but its battery life isn't as good, it has a lower screen resolution, doesn't have a SD card slot (only micro-SD), and it's a bit bulkier given that it has about the same maximum thickness as a MBA but doesn't have its taper. Again, its trackpad also doesn't match the MBA's.
It's also worth nothing that both will obviously won't have a resale value as high as a MacBook Air, won't get you a student discount or a 100$ gift card this summer, and don't have any way to output to a resolution higher than 1920x1080 since they use HDMI output.
In other words, you'd be better off waiting a couple of weeks if you want to find a better value than the current MacBook Air.