Well...I use this:
http://smartphonetracker.blogspot.com/
And it is brilliant. Only thing is that U have to have it installed on the other party's cell phone as well. I often Track my wife and it responds w/ google map location....to Pin-point accuracy instantenously. It is a very nice program.
And you can use it in stealth mode..so the other person doesnt know when u ping them. And thats exactly what sprint-family-locator offers for a fee. This is FREE. The logic is...U send a standard sms (getgpspos, OR u can have any that U like.) ...which makes the other party's phone shoot it's location in lattitude / longitude...and plots it on google maps. U can assign to recieve an email or an sms or both to see the location.
Hope that helps.