The same poisons do pop up in numerous materials/books but if you started today and wrote a scene containing just one compound from just one of several well-known books you'd likely be writing on that book for decades. Or, you'd have a tech manual instead of a novel.
Posions/firearms/explosives...it's not so much what you use in the story, it's how you use it. One of my "specialites" is improvished explosive devices. I will never accurately describe the methodolgy of manufacture or identify the correct measurements/components. I will, however, mention some of the common elements if the story calls for it.
Most common example of a popular book full of errors is probably the first edition of "Anarchist Cookbook" ...full of recipes for all sorts of nasty compounds and devices, and I would suspect at least a quarter of them, if not more, are in error. Close, but no cigar. (Thankfully)
As a fiction writer who may use that book as a resource, I don't have trouble with the inaccuracies, provided the mistake isn't glaring. RE: someone describes a culture methodology for salmonella when it's actually a process for another well-known pathogen. By the same token, I don 't want to read a passge in which the hero "drops the magazine from a .357 model 66 S&W revolver and fires off another 15 rounds."
Of course, this again begs the question, "How techincal do we really want to be, anyway?"
Of course, if that's too cliche for you, read up on the Medicis. Here's a website for ideas, but I'd check references on it. My favorite (and one I used in a medieval fantasy story once) are poisons on coins or other hand-held objects that seep into the skin. If your character-to-be-poisoned handles something in particular every day, you might consider putting a poison on it. (Something akin to The Name of the Rose, perhaps.)
