My husband proposed at a park that was a special spot for us. Just the two of us, he had packed a nice picnic, bottle of wine, my favorite flowers and things to eat. He did it on sweetest day, so I was surprised when he took out the ring. I thought I was just getting a romantic sweetest day picnic. It was intimate and romantic, exactly what I would have wanted. I had made it clear that I didn't want some public proposal in front of my whole family or written on the Jumbo-tron at the Sox game. I think taking her to any place that has special meaning for them as a couple and getting down on one knee can't be beat, even if it isn't exactly original. The other thing that may be good for him is to involve the kids in some way, because she really is saying yes to the whole package.
The only really creative thing I've heard of personally is a friend of mine sent his girlfriend on a scavenger hunt around town to all their favorite places. When she would get to the next place she would get a clue to the next place. (favorite restaurant, coffee shop, book shop...etc) The last clue lead her to a place they had their first date and he was waiting there dressed in full tuxedo with the ring. He has always been creative like this and he did it around her birthday so she wouldn't be suspicious of a proposal at the end. It took a ton of leg work though, organizing the hunt and getting the owners to participate giving her the clues. Very unique and sweet though! Good luck and congrats to your friend =)