• NHibernate home page (NHForge) - link. Download link.
• NHContrib (link) - includes 
• 2nd level cache providers support
• validation
• Getting Started Guide - link. 
• Wiki
• Knol articles (link)
• HQL manual (link)

Helpers:

• A Fluent interface for NHibernate (link to post).
• Getting Started guide (link)
• Source repository at http://github.com/jagregory/fluent-nhibernate
• Sharp Architecture
• Wiki (link)
• Source repository https://github.com/codai/Sharp-Architecture
• NHibernate Query Analyzer (link)
• NHibernate Mapping Generator (link)

• Linq to NHibernate (link). The Linq support is now built in (with version 3).
• HQL AddIn for Visual Studio (link). 
• NHibernate Query Generator (link)
• Spring Framework (link)

• NHibernateHelper, in CreateSessionFactory, add

       sqlConfiguration.Cache(c => c
           .UseQueryCache()
           .UseMinimalPuts()
           .ProviderClass<NHibernate.Caches.SysCache.SysCacheProvider>()
           );
  

• In mapping file (ClassMap), set 
  Cache.ReadWrite(); or any desired value.
• In your code, use or 
  

        var q = Session.CreateQuery("from Department")
            .SetCacheable(true);
   or to
        Session.QueryOver<Department>().Cacheable();

• To cache objects you modify, make sure you use Transaction object and commit changes in transaction.commit(), otherwise they do not propagate to the 2nd level cache. See "Fluent NHibernate and 2nd level cache" article at the link below.

• Quickly setting up and using 2nd level cache (link).
• Fluent NHibernate and 2nd level cache (link).
• Using SysCache as ... (link)

• NHibernate Cache Providers (link).

Retrieving Related Entities from Three Tables

       [Test]
       public void icCleanResults_ThisIsIt()
       {
           var cr = Session.CreateCriteria<Domain.Department>()
               .SetFetchMode("Categories", FetchMode.Eager)
               .SetFetchMode("Categories.Reasons", FetchMode.Eager);

           var result = cr.SetResultTransformer(new DistinctRootEntityResultTransformer())
               .List();

           DisplayContents(result);
       }

This code will retrieve all the data in just one database query and remove duplicate entities on the client side so that operating on the results will be as expected (no duplicate rows as a result of left join query). DisplayContents simply iterates through the Department list and displays the children in a hierarchical tree using simple foreach nested loop.

And now the same thing, using QueryOver:

       [Test]
       public void linqCriteria()
       {
           var l = Session.QueryOver<Domain.Department>()
               .Fetch(d => d.Categories).Eager
               .Fetch(c => c.Categories[0].Reasons).Eager;

           var result = l.TransformUsing(new DistinctRootEntityResultTransformer()).List();

           DisplayContents(result);
       }

However, this *IS* duplicating rows for non-root elements (Categories in this case).

Finally, here is the proper result:

        [Test]
        public void linq4()
        {
            var result = Session.QueryOver<Domain.Department>()
                .Left.JoinQueryOver<Domain.Category>(d => d.Categories)
                .Left.JoinQueryOver<Domain.Reason>(c => c.Reasons)
                .TransformUsing(Transformers.DistinctRootEntity)
                .List();
 
            DisplayContents(result);
        }

In addition to this code, the child collections have to be Sets, not Bags. In the Department, declare Categories collection as

        public virtual ICollection<Category> Categories { get; protected set; }

and implement it as

            this.Categories = new HashSet<Category>();

Then, in the mapping file, use

            HasMany<Category>(m => m.Categories)
                .KeyColumn("DepartmentId")
                .Inverse()
                .Cascade.All()
                .AsSet();

WCF with NHibernate