I'll leave it in the Beginner's section Ed, it's for any fishing topic in that category, but it would have been a good one for the Game section as well.
Darren, I take it you mean flies for stillwaters rather than rivers, otherwise you need a different kind of answer.
Flies I wouldn't be without for stillwaters are a selection of Cats Whiskers, black, white and orange Fritz, green and black buzzers, including epoxy buzzers, a selection of damsels and montanas, and for dry fly, a selection of hoppers and klinkhammers.
Of course there will be many variations of those, and there will be a few flies I haven't mentioned that will be excellent on some waters I don't fish. Another thing, I haven't mentioned quite a few very popular flies, such as Diawl Backs, which lots of trout anglers rave over but which I can't do any good with, so it'll be good if a few trout anglers give you their choices.