Ok, lots to choose from...some may get 2-3 foot. These are mainly herbaceous perennials that will die down in the winter then regrow next spring. Clumps of spring flowering bulbs can be planted between the plants to give early colour.
Dicentra spectabalis
Rose, flower carpet series
Rudbeckia goldsturm
Helenium Moreheim beauty
Phlox paniculata
Kniphofia, popsicle series
Caryopteris worcester gold
Perovskia atriplicifolia
Sedum autumn joy
Alchemilla mollis
Spirea goldflame
Any of the hardy geraniums
Persicaria firetail
fuschia genii
Gaura sp
Monarda sp
Echinacea sp
Euphorbias
Eryngium varifolium
Salvia nemerosa
Coreopsis sp
Rock roses (Helianthemum)
Well there's a few off the top of my head that are worth looking at. I have pretty much all of the above at work and most will flower from july through to frosts, some will flower earlier.
Murrymints...haha, i'm well into herbaceous perennials at the moment. They are easy to grow and care for, they flower for ages if you choose the right ones and are easy to propagate by division. They also come in a wide range of colours, shapes, heights, foliage type, scent and spread.