In a brave mixture of desperation, curiosity, and briefly having the money necessary to indulge, I went out and bought a couple of tentacle monster porn "books" from the Kindle/Nook self-publishing arm of the universe. I picked books that were scored better than halfway (2.5 stars or more out of 5), and those that were explicitly tentacle monster sex books.
Sheila's Tentacle Monsterby Annabel Bastione was the first one, and probably the "best" one, which is saying a lot about how bad the others were. Sheila and her husband, Stan, have a terrible relationship; they can't stand each other, fight all the time, haven't had sex in months. When a crashing noise erupts in their back yard, he goes to investigate, and then she hears screaming. She goes out to find Stan being held upside down and vigorously sodomized by a poorly-described tentacle monster, who then proceeds to work its sexual desires on Sheila instead. The action is literal and highly visual. Sheila's emotional output is all reserved for how much she hates Stan. The "follow up" story is about how Sheila has adopted the monster and takes care of it, followed by her and Stan arguing over who has the "right" to the monster now that Stan has discovered his kink, followed by the monster doing them both, giving Sheila more time to think about how much she hates Stan.
It's more like bad therapy for Ms. Bostione than porn.
My New Boyfriend The Tentacle Sex Beast by Odessa Piper was doing okay. Our heroine finds a book of "sex spells" and decides to try one. The tentacle monster that shows up is bewildered by the idea that Sophie doesn't actually want anything for sex other than a really good lay. She'll take what the monster is offering, but it's not the point. The monster is also a little put out by the assertiveness of the modern woman, but he takes control soon enough. For all that, I just couldn't get past the monster's bad, bad 50s-era greaser/brooklyn/badboy accent. The writer makes the monster less a multi-millennial sexbeast and more a lousy lay from your teenage memories, the pervy boy in the leather jacket who couldn't wait to get his hands on you. I just couldn't get past that.
Alien Tentacle Sex by Pen Penguin was the worst of the lot. It starts with a telling-not-showing "We're a bad bunch of space pirates" opening, then leads into a bloody murder scene on a space station, followed by, well, I didn't even bother to find out. Just bad, bad writing all around.
All of these "books" by the way, are barely stories; the longest was 30 pages, the shortest 18. At $1.99 a pop, that's not horrible, but we should demand more of our tentacle porn stories.
The last time I read decent tentacle monster porn, it was the opening fantasia of Purrfect Plunder, by Andrew J. Offut (1982).
I guess if I want good modern tentacle monster porn, I'll have to write it myself.