I think anything will work as long as it's not a FishEye lens. Just make sure the threads will fit your camera and you buy the best quality lens your budget can afford.
As a general rule price increases with quality. Before I buy a lens I check the reviews and go with the best bang for the buck. Be prepared if you go cheap quality of shots will suffer.
Canon seems to have a series of rather good wide lenses, the biggest being made for 43mm tread - I first got a Kenko ultraHD - made of plastic not even good for a paper weight. The canon is 4 time heavier and $200, pictures are beautiful from the Canon with no loss of contrast.
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