How about Coralbell - they bloom for some time, or take a look at Gallardia (blanket flower) -- they will give you nice color and bloom as long as you keep cutting them back. I like catmint also - and you can shape them anytime - makes a nice mound and consistent color.

Some asters form a low mound, and that would give fall color. Mums, too.

Dwarf balloon flower (platycodon) blooms late and gives nice fall foliage color.

Take a look at perennial geraniums--Johnson's Blue and similar.

Hope that helps!