Here’s a new link to check out, Famous Detectives.
This index of detectives, fictional and real, may not be exhaustive, but it does cover a number of well-known sleuths separated by category. Detective categories include: private investigators, amateurs, police, medical examiner, and TV sleuths. Each sleuth is given a bio page of sorts with info about the character. The inclusion of televised sleuths alongside their print fiction counterparts is particularly nifty.
The site has been around since 2010 and likely will continue to grow and expand. Discover a new detective or track down one you might have forgotten at this site, which has been also added to my links below.
The Poisoned Martini 
That “Famous Detectives” website is *not* a blog.
I don’t think much of anyone writing about fictional detectives who calls Poirot an AMATEUR! He’s a private investigator for hire. He makes his living at solving crimes and that makes him a professional. Also, the site lists Fu Manchu as an amateur detective when he’s a criminal! Nayland Smith is the detective in that series of books. A big raspberry to the person who created that website. Based on those two huge gaffes (I’m sure there are more) I wouldn’t trust anything written there.
You raise an interesting point. The world wide web can be a great resource for information, but any site, including Wikipedia, may contain errors and incorrect details. I should have vetted the site a little better, though I do think it can be a good starting point for discovering new sleuths and being reminded of old favorites. And, case in point, referring to the site as a blog was a typo on my part. Thanks for catching that!