XDA-Shutdown

Again, another nifty utility from over at xda.  You can directly map the long press of the power button to this utility.  It allows you to select whether you want to sleep/restart/shutdown (and you can also disable the confirmation messages for them as well).  It's skinnable so that you can have it match whatever theme you currently are running.

There's also another one called slide to shutdown that has similar functionality but I personally think it's a pain to have to 'slide' to shutdown/restart.