I'm a bit late to the party (very late?), but I'm surprised nobody suggested the Sony A700?! The high iso performance is quite similar to Canon / Nikon, dpreview updated their review using the new firmware. Agreed, it doesn't have fancy live view but since it's been out there for a while, it's quite a bargain! Plus, you came from a Sony a100, so I think you had some lenses already?
Sony has some really nice (Zeiss or old school Minolta) lenses, plus it has image stabilisation for all lenses since the camera has in-body stabilisation.
Anyways, you bought the D90 already. I'm sure you'll enjoy it, it's a great camera!
PS: any nice Sony / Minolta lenses you need to sell?? :-p