Hi, Peter.

   In the mountains of North Carolina, the Steep Slope Law aka Safe Slope Development Ordinance will be a factor.   We own some land in Macon County.   In the year 2004, not far from our land, there was a historic landslide.   Some 15 houses "went down the mountain" into Peeks Creek and a number of people died.   Flooding from Hurricane Ivan (yes, that far north) was to blame.

   Now, before building a house, you need a geo-technical engineer to determine the slope, topography, underlying rock or soil, depth of the foundation, retaining walls, even the angle and grade of the driveway.  

     As for existing homes, perform your Due Diligence!

Selling in my market for 19+ years I do not consider any requirement unique. We have disclosures out the ying-yang. 

The one thing others may find unique is the requirement to disclose a death on a property within the past three (3) years. 

What I find incredibly UNIQUE in my area is a lack of requirement.
It is not required to disclose if a machete massacre or violent murder took place in the house. Fortunately, neighbors are very energized to intercept buyers to present the "Did you know...." conversation starter.
Disclosures regarding sinkholes and settling of 70 year old houses seems to scare the 'bajeebies' out of uninformed buyers. But in about .07 nanoseconds the next buyer makes an offer.

Not really.  All the disclosures are pretty well known and used all the time.  We typically always do  termite report as there are 2 types of houses in AZ - 1 that has termites and one that might get them.  Also, of course septic systems are required to be inspected.  Seller fill out a very extensive disclosure form and we also had a Buyers Advisory that is a gazillion pages long (not really but buyers think it is) with any kind of inspection or test one could think of plus more.

As Richie Alan Naggar, alluded, we, a seller in California is required to provide a Natural Disclosure Statement to a seller. The NHD reports includes information about nearby earthquake fault lines, landslide areas, potential flood areas due to dam failure, fire zones, and more. Sellers are also required to complete additional questionnaire forms.

And, Susan Emo, while buyers are expected to due their own due diligence, who is going to know more about a home than the people who live there?

Here in Ontario, Sellers are 'asked' to complete a disclosure statement, Seller Property Information Statement (SPIS) sometimes at the request of the Buyer.  I've not yet come across a lawyer who will advise the seller to do so. If you do answer, you're most likely ending up in court.  Sellers are not experts when it comes to their home.  Buyers must do their own due diligence.    From our very own AR @BrianMadigan To Sign or Not to Sign

I tend to leave that to the Hazard report which I order into escrow

Interesting question.  I have not experienced any unusual disclosures other than something that a seller did not disclose and I had to because of my seeing something the seller was not willing to disclose.

Section 10-702 of Maryland's Real Property Article states that a seller must disclose the latent defects in their property to the buyer. Latent defects, in this context, refer to the kind of defects that the buyer might not be able to spot during an inspection.

We live on a lake with 4 types of ownership.... fee simple, strip lease, residential access lease and full lease lots.  It's a pretty important disclosure that agents from other areas often don't get right.

On our IL property disclosure seller must answer whether the house was ever a meth lab.

Great question Peter Mohylsky. BRIX REALTY 

These are so normal to a Californian, but they do often scare my out-of-state buyers: we have seismic zone and wild fire disclosures.
And if or when the buyers raise an issue over them, I share with them and point East or North that Arizona or Oregon are nice second choices for residency, "cause you ain't avoiding either in Cali!" Although I can help you avoid the high fire areas, seismic happens.

We have a disclosure for the airport. They measures the decibels of noise and created contours. If a home is in a particular contour, you have to disclose it. There is also a toll road being finished. If a property is close to the road we disclose it. Our seller disclosure has a standard question about noise. So private airports, trains, etc. would be disclosed there.

Great question with multiple answers. It all depends on what area you serve and what local or state ordinances or statutes require. Some excellent responses!

In Oregon the disclosure requirements are written by the state legislature.  We are required to disclose what is in this - and it doesn't require us to disclose death in a home.

We have a disclosure document that pretty much walks sellers through things they should be disclosing and it is all-inclusive.

Sounds similar to our lakeshore setback requirements.

Utah lies on a fault line and that is in the REPC, also we have a Wire Fraud Disclosure, warning people of the dangers of wiring funds, also the Seller's Property Condition Disclosure that is filled out completely by sellers, signed and dated, then sent to buyer's for signatures and dates.

Our homeowners need to disclose anything they are aware of, including if meth was ever used in the property.

We were required to ask sellers if the house was haunted.

We have a "Statewide Disclosure" that is 16 pages long.  Some cities have their own 3-6 page disclosures on everything from protected trees to agriculture to you name it.  Then we have the transaction disclosures that want to know if you've ever had a pest control service.

It's hard to say you weren't informed in California, that's for sure!

In an adjacent county, they have a requirement to cap a wood burning fireplace (which everybody seemingly removes the cap shortly after acquiring the property). 

We don't have anything too strange. There are questions regarding radon and the location of the oil tank. You can't convey property with an underground oil tank, it would need to be removed and a new one installed (usually in the basement or in the garage); soil would need to be tested by the state. High radon levels would need to be remediated.