Recent approaches to a much-covered subject...
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.