There was a beautiful vinca out this year that I put in pots on my porch--green and white variegated leaves(about half of each color on each leaf, so very ornamental and showy for a vinca) with red stems--drapes nicely--does well in both sun and shade. Also cuphea "Tiny Mice" will drape in part shade, although it is a full sun plant, too.

Also trailing coleus--I think "Inky Fingers" is one of them. I haven't planted any myself but have seen them. Very beautiful trailing on the edge of containers and windowboxes.

There are super lobelias out now, too, that do well all season, withstand the heat, and have larger flowers, clouds of trailing blue blossoms.

These are Provem Winner or Proven Selection plants, for the most part, except for the coleus.

How much shade are you talking about? I planted verbena in window boxes along my back deck that get indirect sun all day and a few hours of direct afternoon sun (2-4pm)- they've bloomed all summer but instead of being compact 6" plants they are leggier more like 10" or so. The butterflies love them.

Torenia is sort-of a trailer, does well in some shade (mine get about an hour of sun in the early afternoon, then dappled for a few hours).

Non-trailers: Impatiens and Begonias (of course), Browallia.