One of my favorite blogs is the
Dapper Cadaver - Monster Mondays. It covers everything from movie monsters to cryptozooligical mysteries, to real news stories that would be very Winchester worthy.
Some of my favorite past entries include:
Dolichocephaloids "Peruvian coneheads"
Because these skulls are over 2,000 years old, I can't imagine them being a Winchester gig but I could see them being part of the mythos in the boys' world, possibly being an ancient demon race that somehow ties into the apocalypse or something Sam comes across on the internet or in a reference book while looking in to a current mysterious creature.
Vampiric creatures All about creatures that are similar in nature to the the concept of vampire whether by drinking blood or in one incredible case, a deer that has retractable fangs.
Not Another Bigfoot Scam More season 1-ish in style, but I could totally see the boys having been all over this. Only on the show, it would have been real. ;)
The Monster of Troy This was one of my favorite entries. No one knows for sure what exactly it was, there are just many theories, and I like how this particular entry goes over a lot of the options and allows you to draw your own conclusions since in all likelihood, we'll never know for sure. It reminds me a lot of the boys' process in monster-of-the-week type episodes; looking at vague pictures then comparing them to what they know is out there and trying to narrow it down from there.
The Montauk Monster Now this would have definitely made the boys' radar! Last year, this turned up on a beach near Long Island, NY. The creature was photographed by a few witnesses by then stolen by a local so that all anyone had to go on was photographs. This caused a lot of speculation and sensationalism but was eventually revealed to by a marketing stunt by an upcoming movie which was disappointing but the history of speculation is very interesting and revealing:
http://en.wikipedia.org/wiki/Montauk_Monster I could go on and on with the links, there is just that much of interest on the site especially for people who enjoy the mythological aspects of SPN. I spent many a night of insomnia, reading the entire blog backward and forward and still go revisit it when my brain could use a little imagining. They've also got a store where they sell all kinds of Halloween props and all kinds of other bizarre paraphernalia that would work perfectly for the SPN props department.
Definitely check it out when you get the chance, and feel free to share in the comments anything you find that you could see as being Winchester-worthy.