I have used all kinds of trailing plants in my pots and window boxes with impatients. Asparagus fern is lovely and English Ivy works. I have used lobelia and baby's breath that begins to trail as it matures. The impatients will begin to hang over edges as well. To see examples of my windowboxes and baskets you can go to webshots.com, community, gardens. Today my pictures are at the bottom of page 4 under vignewood. Good luck. Putting these combinations together is such fun.

Thanks so much. Your pictures are beautiful--all sorts of great ideas. I ended up (before I saw your post) using lamium as a trailer. Also I used some verbena, dwarf coleus and one other small pink-leaved plant whose name is escaping me. (Of course I got too many plants and had to do 2 additional smaller containers as well.) My main problem now is that the (double) impatiens appear to be growing at the double the rate of everything else, so may have to be transplanted to a flower bed soon.
Thanks again for sharing your pictures!

This year I'm using torenia (blue) with my impatiens (white) :)

Lysmachia, torenia, trailing coleus, ivy, vinca vine,

Blue lobelia is very pretty with impatients.