Manipulating Model/Table/Controller Names in Rails

There are some very useful methods that operate on the names of your models, tables and controllers in Rails. I use them infrequently enough that I have to relearn them every time - so I'm putting them in here:

Given a string with the name of a model (e.g. Project), how can I create an ActiveRecord call on the fly using that model?

str = 'Project'
project = (str.constantize).find(1)

How can I get the name of the corresponding controller ?

controller = str.tableize

Given a string with the name of a controller, how can I get the name of the Class/Model ?

str = 'sales_contact'
model_name = str.camelize

I the string is plural:

str = 'sales_contacts'
model_name = str.classify

How do I do the reverse operation?

str = 'SalesContact'
name = str.underscore