How to get Twitter-Bootstrap navigation to show active link?

Just made an answer on the very same question here Twitter Bootstrap Pills with Rails 3.2.2

<ul class="nav">
  <li class="<%= 'active' if params[:controller] == 'controller1' %>"> <a href="/link">Link</a> </li>
  <li class="<%= 'active' if params[:controller] == 'controller2' %>"> <a href="/link">Link</a> </li>
  <li class="<%= 'active' if params[:controller] == 'controller3' %>"> <a href="/link">Link</a> </li>        
</ul>

You can use something like (very similar to what @phil mentioned, but a little shorter):

<ul class="nav">
  <li class="<%= 'active' if current_page?(root_path) %>"><%= link_to "Home", root_path %></li>
  <li class="<%= 'active' if current_page?(about_path) %>"><%= link_to "About", about_path %></li>
  <li class="<%= 'active' if current_page?(contact_path) %>"><%= link_to "Contact", contact_path %></li>
</ul>

https://github.com/twg/active_link_to

<%= active_link_to 'Users', users_path, :wrap_tag => :li %>

#=> <li class="active"><a href="/users">Users</a></li>

I used a helper to implement this in the style of Rails' form helpers.

In a helper (e.g. app/helpers/ApplicationHelper.rb):

def nav_bar
  content_tag(:ul, class: "nav navbar-nav") do
    yield
  end
end

def nav_link(text, path)
  options = current_page?(path) ? { class: "active" } : {}
  content_tag(:li, options) do
    link_to text, path
  end
end

Then, in a view (e.g. app/views/layouts/application.html.erb):

<%= nav_bar do %>
  <%= nav_link 'Home', root_path %>
  <%= nav_link 'Posts', posts_path %>
  <%= nav_link 'Users', users_path %>
<% end %>

This example produces (when on the 'users' page):

<ul class="nav navbar-nav">
  <li><a href="/">Home</a></li>
  <li><a href="/posts">Posts</a></li>
  <li class="active"><a href="/users">Users</a></li>
</ul>