Our 2003 Nissan Pathfinder won't start tonight.  It is an automatic. 
It just makes a rapid electronic clicking sound when I turn the key
but nothing happens from the engine area.  Seems electrical.  Any
suggestions?  Also how do I get it out of gear to back it our for a
tow truck if I need to...

Sounds like a dead battery, did you leave the dome light on inside,
how about something plugged into the 'accessory socket'...I've done
that!

Dead battery, have someone jump start you.

Turn the key to start, put your foot on the brake, shift it out of
park into neutral.

I just tried jumper cables and no difference.

a) I would not try to jump start any modern car; too many transistors
and semi-conductors to blow.
b) I have heard that a dead battery can act as a short to the jumping battery.
c) Make sure that all connections in the battery circuit are clean and tight.
d) the starter or starter switch; usually all together in one unit

Tow truck got it started and got it to the shop - something strange
going on with the battery.

Thanks for all your advice!

Might be something wrong with the solenoid or a part-broken starter
that when you last started the car, the starter disk? stopped at the
half broken part and now it's stuck. A dead battery would not make any
sound at all. The fact that the starter is still trying to start,
shows the battery is still good. Also if you have any after market
alarms that is tapped into the starter and/or ignition wiring harness,
there might be a conflict.

I've got an '03 Pathfinder that has inconsistent starting problems. I
have 42,000 miles and am now on my 3rd battery. I'm having the same
experience where I try to start it in the morning (after driving it
the previous night and parking in a heated garage) and I just get the
rapid clicking. I just had the battery replaced about a month ago, and
this has already happened again. I've had Midas (the people who put
the battery in) test it for a draw and they can't find anything. It's
really getting frustrating to not know if I can count on my car to
start. And of course, this happens enough and it kills another
battery.

I have a Circut City installed remote starter installed, but remember,
Midas has tested for a draw and can't find one. And this problem
started ocurring well after I had the remote starter installed. On a
couple rare occasions, I have caught the headlights not turning off
when they should (in the 'Auto' mode). For example, when I exit a
tunnel (where the lights have turned themselves on) and go back into
full daylight, the headlights don't turn themselves back off. As many
times as I've tried to check my headlights down in the garage (to make
sure they turn off) they've turned off. But I haven't checked them any
of the times I've ended up with a dead battery. It's getting very
frustrating as this problem is a very intermittent one. I've never
left the dome or any other lights in the car on.