I recently made the switch from a Canon 20D to a Fuji S5, and as such bought all new lenses. I don't have any experience with Fuji/Nikon products and need to buy a backup camera. I'm not able to buy another S5 right now, and would like to spend no more than $500-$800.

I am considering:
Fuji S2
Nikon D50
Nikon D70
Nikon D70S
Nikon D100

I've ruled out the D40 because of lens compability issues.

I've heard stories and rumors of bugs in certain models, and am hoping to tap in to the wealth of knowledge that lurks on this forum!

Thanks...

I would go for the nikon d70. The fuji S2 is really slow at focusing.

I would say the D70 or D70S. They're not bad cameras and great for a back up just in case.

I have a D100 (actually 3) with vertical battery grip that I will sell, if you are interested. It is LN to Mint. Excellent cameras.

I just recently bought an S5 also.

I think you ought to pay the extra for a D80 or D200.

The D80 may be a little awkward since it takes SD rather than CF cards, but the D200 is an great camera if you want to drop the $$. It sounds like the OP would rather spend a bit less on the backup gear though.

Thanks, everyone, for the feedback!

I'd get a D200 for a backup camera. Now that the D300 and D3 have been announced, you're sure to find some good deals on used D200s on ebay and the like. The D70 is a good runner up but I'd stay clear of the D100. It's a decent camera but not professional in any way shape or form. It's terrible at shooting RAW and quite quirky in other areas. As a backup to a Fuji I wouldn't recommend it. Look out for a D200, you'll love it.