my_controller.rb

class MyController < ApplicationController
  def show
    @sysinfo = SysInfo.new(model_stuff, ...)
  end
end

show.html.haml

%h1 A page of stuff

%h2 A list of members

= @sysinfo.render_members_on(self)

%h2 A list of events

= @sysinfo.render_events_on(self)

sys_info.rb

class SysInfo
  def initialize(model_stuff, ...)
    # find things and calculate stuff
  end

  def render_members_on(template)
    return '' unless @members.length > 0
    template.render(:partial => 'path/to/members_partial', :locals => {@stuff})
  end

  def render_events_on(template)
    @events.each do |event|
      template.render(:partial => 'event/details', :locals => {...})
    end
  end
end