What is the syntax for self referencing foreign keys in EF Code First?

Something like this will work:

public class Contact
{
    public int Id {get;set;}
    public string Name {get;set;}
    public int? SpouseId {get;set;}

    [ForeignKey("SpouseId")]
    public Contact Spouse {get;set;}
}

ForeignKeyAttribute has been added to System.ComponentModel.DataAnnotations by CTP5 assembly.

Update I: CTP5 Bug:

Due to a bug in CTP5, creating an Independent Self Referencing Associations throws an exception. The workaround is to use Foreign Key Associations instead (which is always recommended regardless).

Update II: Using Fluent API to Configure a Self Referencing Association:

You can also use fluent API to achieve this, if you prefer:

public class Contact
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int? SpouseId { get; set; }                

    public Contact Spouse { get; set; }
}

public class Ctp5Context : DbContext
{
    public DbSet<Contact> Contacts { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Contact>()
                    .HasOptional(c => c.Spouse)
                    .WithMany()
                    .HasForeignKey(c => c.SpouseId);
    }
}

Working with the Model:

using (var context = new Ctp5Context())
{
    Contact contact = new Contact()
    {
        Name = "Morteza",
        Spouse = new Contact()
        {
            Name = "Code-First"
        }
    };
    context.Contacts.Add(contact);
    context.SaveChanges();
}