View:

<%= title "Forgot Your Password?", :h2 %>
<% form_for @password do |f| %>
  <%= f.error_messages %>
	<% f.field_set "Enter Your Email Address" do %>
	  <%= f.text_field :email %>
  <% end %>
	<%= f.submit "Submit" %>
<% end %>

Controller:

class PasswordsController < ApplicationController
  def new
    @password = Password.new
  end

  def create
    @password = Password.new(params[:password])
    @password.user = User.find_by_email(@password.email)

    if @password.save
      PasswordMailer.deliver_forgot_password(@password)
      flash[:notice] = "A link to change your password has been sent to #{@password.email}."
      redirect_to :action => :new
    else
      render :action => :new
    end
  end

# ...
end

Model: