helper.rb

def table_listing(collection, &block)
  row = RowHandler.new
  capture(row, &block)
  headers = "<tr>" + row.columns.map {|name, proc| "<th>#{name}</th>" }.join("\n") + "</tr>"
  
  if collection.empty?
    rows = "<tr><td colspan=\"#{row.columns.size}\">Ingen treff</td></tr>"
  else
    rows = collection.map do |item|
      output = "<tr>"
      row.columns.each do |name, proc|
        output << "<td>"
        #output << proc.call(item) - this failz
        output << "this is a row"
        output << "</td>"
      end
      output << "</tr>"
    end.join("\n")
  end
  
  concat(content_tag(:table, headers + rows), block.binding)
end

class RowHandler
  attr_reader :columns
  def initialize
    @columns = []
  end
  
  def add(name = nil, &block)
    @columns << [name, block]
  end
end

view.erb

<% table_listing @users do |c| %>
  <%= c.add('Username') {|u| link_to(u.username, user_path(u))} %>
  <%= c.add('E-mail')(&:email) %>
  <%= c.add('Full name')(&:full_name) %>
  <% c.add do %>
    <%= button_to 'Destroy', user_path(u), :method => :delete %>
  <% end %>
<% end %>