Here's a short story competition with £100 prize. The theme is fall. (Note that all shortlisted entries will be published.)
This writing competition has an unusual prize - 10 hardback copies of their book printed. There's also an Amazon voucher for the runner up. Theme is Autumn.
There's another short story competition. The prize is £500 and an Arvon course. The theme is Freedom.
Rather read short stories than write them? My collection is still free.