Lack of certainty about what the parties' rights and obligations under the contract are.
Either the common law or statute makes it illegal.
Lack of some required formality.
Lack of legal capacity to enter into a binding agreement.
Hire purchase agreements.
Contracts for the transfer of shares in registered companies.
Contracts for the sale of land.
Conveyances of land
Leases of land for a period of more than three years.
Here's an interesting quiz for you.