At novel length, I'd have to say some of the very best faux-Holmes are done by Nicholas Meyer (yes, the movie director), who wrote the thoroughly brilliant
The Seven Per-Cent Solution, which was also made into a movie, and two other novels which are fairly good, though not nearly in the same league.
Canadian SF writer Robert J. Sawyer's
You See But You Do Not Observe is a really good short story which he makes available for
free online reading at his website. It's won a number of awards.
Neil Gaiman's
A Study in Emerald (
downloadable from his website in PDF) is a marvelously inventive Lovecraft/Holmes mythos mash-up. If you happen to like such, I notice that the anthology it was originally published in,
Shadows Over Baker Street, is now available as an e-book (but rather pricey, and the overall contents are really only worth MMPB equivalent, IMHO).
Titan books have been
re/e-printing various Holmes/public domain mash-ups. Quality varies, but some are quite good, and I've read and reviewed (no spoilers) a few in
my book list for the 100 books reading challenge.
Available for a very affordable price is Nightshade Books' anthology
The Improbable Adventures of Sherlock Holmes, which reprints some of the better previously published sf/fantasy/horror takes on Holmes. It's DRM-free for
only $6 from Baen and you can buy it in a
bundle of other unrelated Nightshade books for an amortized cost of $5. Also, you can try before you buy the downloadable sampler "
Selections from" which lets you read a handful of the stories in the format.
A possible low-cost one to try (have not read it myself) is
Sherlock Holmes in America, only $1.99 on Kindle at the moment (
not sure if this is special CyberMonday sale or "regular" markdown promotion part of "The Big Deal sale", good until Dec 3rd according to the Amazon ad blurb). This has stories by a number of people who also write longer-length Holmes pastiches, so could be useful for sampling. I was thinking of getting it myself when it was on 99 cent sale a few months ago, but forgot about it until the price had gone back to $9.99. Though personally, I'm going to wait to see if it drops back down, since Skyhorse seems to be running intermittent 99 cent sales on their titles (unless it's an Amazon event thing, in which case it'll probably show up on sale again in the future).