flowers for 1 year

Cosmos, Cleome, summer stocks.....................oh, too many to mention 

Look at Sarah Raven's site for good combinations/ideas
http://www.sarahraven.com/flowers/seeds/annuals

Then look at other seed suppliers as hers are usually more expensive than elsewhere (though you can often find hers cheap on ebay  )

Globe amaranth, cockscomb, poppies, snapdragons and sunflowers?

Chrysanthemums as well - as jaydig says - check for flowers that last well in a vase.

Thanks guys, some great ideas. There's such an array of flowers out there I just did not know where to start 

I know that a huge range of flowers have been mentioned already but I would suggest that you don't dismiss bulbs/corms and tubers.Gladiolaii and dahlias are quite happy to be lifted up in autumn,stored over winter and planted in a new bed next year

Also, let me throw in Higgledy Garden seeds. Gurgle it, all cut flower seeds.

I had a look at this site, and couldn't resist making an order. It's just arrived, together with a handwritten letter apologising for the fact that they were out of stock of one of the seeds I ordered, but saying they have substituted it with another variety of the same seed, and also sent two free packets of other seeds too. Brilliant, personal service, and a good choice of out of the ordinary cut flower seeds to grow. Can't wait for the summer!