As fit as a fiddle and the others:

As strong as an ox – very strong

As strong as nails – very unfeeling; able to bear hardships

As busy as a bee – very busy

As sure as fate – certainly

As hungry as a hunter – very hungry

As thick as thieves – very friendly: They didn’t like each other at first, but they’re thick as thieves now.

As old as the sea / as old as the hills – very old: My husband’s great-aunt is as old as the hills, but she ‘s very fit.

As slow as a snail – very slow: It’s no use to hurry him up, he’s as slow as a snail.

As frank as the day – quite clear: There’s nothing to worry about, because everything is as frank as the day.

As brown as a berry – well tanned

As red as a lobster – very red (about skin): I’d like to get as brown as a berry, not as red as a lobster.

As blind as a bat – completely blind: Without his spectacles, he’s as blind as a bat.

As clear as a bell – very easy to hear: His voice was as clear as a bell, although he was phoning from South America.

As sound as a bell – undamaged and in very good condition – Although the boat was old, it was as sound as a bell.

As black as pitch – very dark: It was pouring with rain, and the night was as black as pitch.

As dry as a bone – completely dry: “Is the ground wet?” – “No, it’s dry as a bone.”

As tough as old boots - very tough or strong, esp. in health: He can walk in light clothes in winter , ‘cause he’s as tough as old boots.

As bold as brass – very bold, usu. impertinent – She walked in late as bold as brass.

As calm as a millpond – very calm – The sea was as clam as millpond.

As cold as charity – very cold – I was as cold as charity in the cinema.

As clean as a whistle – very clean or clearly: Everything in her kitchen was as clean as whistle.

As clear as crystal – very clear, easy to understand: The water was as clear as crystal. The instructions were as clear as crystal.

As clear as mud – not at all clear: He’s explained to me twice how to do it; but it’s still as clear as mud.

As regular as clockwork – perfectly regular(ly): He comes round for tea at half past 3 every afternoon, as regular as clockwork.

As lively as a cricket – very lively: My great-aunt is ninety-two, but she’s still as lively as cricket.

As fresh as a daisy – very bright, active: After a night without sleep we were exhausted, except Ann who was as fresh as a daisy.

as fresh as a cucumber – feeling well

as happy as the day is long – very happy, in how one is spending one’s time – In summer children spend their whole time in the orchards, as happy as the day is long.

as happy as a lark – very happy – The little girl spent the afternoon digging on the beach as happy as a lark.

as happy as a sand-boy – very happy and cheerful – My husband is as happy as a sand-boy when he’s working on his car.

as dead as a/the dodo – completely dead or no longer fashionable, useful, popular – That kind of hairstyle is as dead as a dodo.

as dull as ditchwater – very boring or uninteresting – The lecture was as dull as ditchwater.

as pure as the driven snow – completely pure – I don’t care whether she’s evil or as pure as the driven snow.

as drunk as a lord – very drunk – He went out to a reunion last night and came home as drunk as a lord.

as easy as falling off a log – very easy – The machine is so well-designed that learning how to use it is as easy as falling off a log!

as fit as a fiddle – extremely healthy – He is eighty-eight, but he is as fit as a fiddle.

as good as gold – (usu. of children) – very well-behaved – Their little girl is as good as gold when they take her out visiting.