As our winters become ever more unpredictable, the perennial form of Lobelia (ie. Lobellia Cardinalis or siphilitica) is probably better in a pot, as you can move it to a more sheltered/protected spot for the winter. They are thirsty plants though, so consider this when planting up.
Penstemon 'Huskers Red' does very well in a pot too, & I'm sure that some of the more tender penstemons would be suited to container growing for much the same reasons as the Lobelias.
Mimulis cardinalis also does well in pots (& self seeds prolifically), but like the Lobelias is thirsty.
Not sure about how big a pot you were considering, but if you wanted to go big & could give it dry winter storage (ie. in the garage), how about Brugmansia?