My landlord, without warning, consulting or informing me, sold the house in which I rent an apartment to a developer who is building a new fast food joint on the lot next door. My rent is paid month to month but the other tenants here have signed leases through August 2013. The sale is expected to close in December, at which time I fear eviction. What rights, if any, do we have? Must my neighbors leases be honored since they have written leases? Can I ask for a written lease as well to give myself some legal protection like what they have? Since we are being forced to move against our will, is the developer under any obligation to assist us with moving costs?

Laws vary by state (in the US).
Your owner was not required to inform you of the sale. A new owner must honor a lease (there are certain exceptions when in foreclosure). You, being month to month, can be told to leave in most states in 30 days. You can ask for a lease, but there is nothing you are entitled to by law. The owner does not have to pay for moving. Often a new owner will offer enticements to those with leases, including moving, however. The only bargaining power you have is something like a promise to pay right until the day the last of the other tenants moves out, in exchange for reduced rent or a lump sum, but don't count on it.

The new owner must honor any written lease, since you are on a month to month rental, you may be asked to leave with a 30 to 60 day notice depending on where you live.

The new owner will be responsible for giving you back your deposit. There is no reason the owner would give you a lease. In fact I doubt it, since the sale is already agreed, and part of it would be who has and who does not have a lease.

If the new owner wants them out, he will have to buy out their lease. Or he may just wait until their lease runs out.

You have gotten correct legal advice so far, though knowing your location (ANY question on law needs to include your general locale as laws vary by area. ) might help us find some legal protection, though I doubt it.

What I'm wondering is why you thought your landlord had to inform of the pending sale? And why you think you have some right to to not be forced to move from a rental?

When you rent, you are subject to the terms of your lease. When you decided to go month to month (or were given no other choice), then you needed to be aware that your tenancy could be terminated with proper legal notice, usually 30-60 days.

You and the other tenants have no legal protection other than your leases. Never did.

The good news, is that the new owner cannot start demolition until the last tenant has moved. So if some tenants have leases until August, then you may have some time to find a new place. But if the developer decides to buy them out you may have less time. Since the sale won't be finalized for at least another month, I'd start looking for a new place.