Raspberries don't mind the shade if you fancy those. Rosemary and thyme will stay green all year around. I like clematis, and climbing roses are lovely too. Salvias are nice and don't need much water. Bamboo will take a lot of water, and so will acers (we had to take one of ours in during the heatwave, the top of it burnt). Olives and bay are other evergreen options. Ferns are gorgeous especially if done as under planting under a tree with some foxgloves. DH did a little corner like this and it felt quite cool to be there during the heat although it wasn't actually any cooler! We're planning to put a small water feature there.
DH swears by buying perennials, as pp said above with bedding plants you're buying them every year. Plenty of beautiful flowering shrubs. Although we have a hollyhock this year that's a beauty.
Lots of things can be grown from seed in small pots on your window sill. Sunflowers, peas, beans, lupins, hollyhocks are a few that will give height for next year and take the bare look off the wall.
Asian lilies grow pretty tall when they're etablished and you just buy the bulbs. Dahlias are lovely, they grow from tubers like potatoes. The ones called after different bishops are my favourite.
Speaking of bulbs, you could be thinking about snowdrops, crocuses, daffs and tulips now.
Osteospernum are another lovely perennial (not sure how they'd do in frost) but asters should manage frost fine (alpine type things). They are low in height.
How wide is the bed?