Not exactly sure what kind of pots you mean, a picture might be useful.

Perhaps some trailing plants, like trailing lobelia. There is a list of trailing plants here:
http://gardening.about.com/od/containergardening/a/ContainerPlants_4.htm

This time of year I use a lot of geraniums.

The same as you would in a hanging basket, guest. Petunias, Surfinias, Bacopa, Nemesia, Nasturtiums, and yes, Pelargoniums are great as the centre plant with trailing ones round it. These are all sun-lovers.

I have a Heuchera in mine, with violas in as well.

I have trailing begonias in my wall pots which I get from the internet as plug plants do the pots early and leave in greenhouse or other frost free place put out when frost are no longer a threat express