You probably know that I’m a big fan of Slyce Software’s Visual NHibernate. To me, it is the best tool for generating your entities and mappings from an existing database (it also allows you to go the other way, but I honestly have never used it that way).

What I like most about it:

• Great support: folks at Slyce always listen to your suggestions, give you feedback in a timely manner, and I was even lucky enough to have some of my suggestions implemented!
• The templating engine, which is very powerful, and more user-friendly than, for example, MyGeneration’s; one of the included templates is Sharp Architecture;
• Advanced model validations: it even warns you about having lazy properties declared in non-lazy entities;
• Integration with NHibernate Validator and generation of validation rules automatically based on the database, or on user-defined model settings;
• The designer: they opted for not displaying all entities in a single screen, which I think was a good decision; has support for all inheritance strategies (table per class hierarchy, table per class, table per concrete class);
• Generation of FluentNHibernate mappings as well as hbm.xml.

I could name others, but… why don’t you see for yourself? There is a demo version available for downloading.

By the way, I am in no way related to Slyce, I just happen to like their software!