The only Pastiche I've read was The Seven Percent Solution by Nicholas Meyer. I enjoyed that book greatly, and would like to seek out more sometime. I know Meyer wrote a few more himself. As for the Sherlock Holmes Canon, I just have a paperback edition, but the New Annotated editions look very interesting.
Meyer wrote two more.
The West End Horror has Holmes palling around with George Bernard Shaw and Oscar Wilde. Contrary to popular belief, this book does
not involve Holmes hunting down Jack-the-Ripper.
About ten years ago Meyer wrote a sequel to
The Seven-Percent Solution entitled
The Canary Trainer. Holmes has come to Paris during "The Great Hiatus," and he takes up the violin at the Paris Opera House. However, something lurks in the sewers beneath the Opera House, and people report seeing a Phantom.
I enjoyed
West End.
Canary Trainer less so.
There's a much better Holmes/Phantom crossover in Sam Siciliano's
The Angel of the Opera.
Loren D. Estleman wrote two very good crossover pastiches --
Sherlock Holmes vs. Dracula and
Dr. Jekyll and Mr. Holmes are exactly what their titles promise. Of the two, I prefer the former; Estleman does a credible job inserting Holmes into the events of Bram Stoker's
Dracula.
Holmes and Dracula tangle again in Fred Saberhagen's
The Holmes/Dracula File.
Manly Wade Wellman wrote a book called
Sherlock Holmes' War of the Worlds. Nice concept, goofy execution. (Holmes and Mrs. Hudson? Say it ain't so, Joe!)
Holmes battles Jack the Ripper in Michael Dibdin's
The Last Sherlock Holmes Story and Edward B. Hanna's
The Whitechapel Horrors. Oh, and in Ellery Queen's
A Study in Terror as well. Hanna's book hews the closest to the actual Ripper murders; Queen's book features two of the canonical murder victims, and Dibdin's book is incredibly shocking.
A Canadian small press published a
Star Trek/Sherlock Holmes crossover anthology a few years ago,
Federation Holmes. Despite having Holmes meet Kirk and Spock, the book has the
Enterprise-E on the cover.
Mike Ashley put together an anthology about ten years ago called
The Mammoth Book of New Sherlock Holmes Adventures. It's what the title suggests -- some thirty new stories of Holmes by writers like Michael Moorcock, Stephen Baxter, Peter Tremayne, and others. I'd recommend it.
Larry Millett wrote a series of novels about Sherlock Holmes' adventures in Minnesota. Every couple of months, Holmes would go to Minnesota to solve a crime in the Twin Cities and the surrounding area.
Marvin Kaye's anthologies are generally quite good.
The Game Is Afoot is a nice collection of Holmes parodies, pastiches, and scholarly work from the 1800s to the 1990s.
Resurrected Holmes is a lot of fun -- it purports to be an anthology of Sherlock Holmes stories written by the likes of Ernest Hemingway, H.G. Wells, and a dozen more.
Shadows over Baker Street is an anthology of Holmes vs. the Lovecraftian mythos. Peter Cannon's
Pulptime covers similar ground. (Cannon also wrote the Wodehouse meets Lovecraft story, "Scream for Jeeves.")
I would love to get my hands on Ellery Queen's
The Misadventures of Sherlock Holmes from 1943.
Oh, and Adrian Conan Doyle's anthology
The Exploits of Sherlock Holmes is pretty good.