Fujitsu LifeBook Q2010 is about .5mm thinner.
.5mm thicker, it also doesn't thin towards the front (so its volume is quite a bit more), or have nearly the same specs (1.2ghz Core Solo ULV versus 1.6ghz Core 2 Duo). It is 6 months old, though.
Personally, I think the Air came along too soon - the form factor is great, but it really needs the SSD, which is way too expensive for not much space right now. 1.8" drives just don't cut it. The Mac Book Pro is probably a better machine (and not that much bigger - 1.0" tall level).