Michael Kirkham for White's Books (see also here):

Coralie Bickford-Smith for Penguin (see also here):

Unknown for Vintage Classics UK:

Unknown for Atlantic Crime Classics (see also here):

And finally, Glen Orbik for Hard Case Crime (see also here):

UPDATE: Karen Horton, no mean designer herself, points me towards two more recent Holmesian covers.
The first is by Jen Wang, for Penguin US:

The second is by Rob Grom, for Thomas Dunne Books:

UPDATE 2: Regarding the Hard Case Crime cover, the ever-wise Tulkinghorn points out this extensive discussion of it with the publisher here, which also refers to this Orwell cover.
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