examples.erb

<% list_items_for @products do |product| %>
  <%= link_to product.name, product %>
<% end %>

<!--
  <li class="first"><a href="/products/1">Product #1</a></li>
  <li><a href="/products/2">Product #2</a></li>
  <li class="last"><a href="/products/3">Product #3</a></li>
-->

<% list_items_for @products, :class => "product" do |product| %>
  <%= link_to product.name, product %>
<% end %>

<!--
  <li class="product first"><a href="/products/1">Product #1</a></li>
  <li class="product"><a href="/products/2">Product #2</a></li>
  <li class="product last"><a href="/products/3">Product #3</a></li>
-->

<% list_items_for @products, :class => lambda { |p| "active" if p.active? } do |product| %>
  <%= link_to product.name, product %>
<% end %>

<!--
  <li class="first"><a href="/products/1">Product #1</a></li>
  <li class="active"><a href="/products/2">Product #2</a></li>
  <li class="active last"><a href="/products/3">Product #3</a></li>
-->

list_items_for.rb

def list_items_for(collection, opts = {}, &block)
  if collection
    opts.reverse_merge!(:first_class => "first", :last_class => "last")

    try_call = lambda do |obj, item|
      obj.respond_to?(:call) ? obj.call(item) : obj
    end

    concat(collection.map { |item|
      attributes = {
        :class => [
          try_call[opts[:class], item],
          (opts[:first_class] if collection.respond_to?(:first) && item == collection.first),
          (opts[:last_class] if collection.respond_to?(:last) && item == collection.last),
        ].compact * " "
      }

      if opts[:attrs]
        attributes.merge! try_call[opts[:attrs], item] || {}
      end

      content_tag (opts[:tag] || :li), capture(item, &block), attributes
    }.join("\n"))
  end
end