I feel kind of odd that I have never read an old book containing a legend about a dragon or goblins. Do such things even exist? I assume they've been translated from old english or something right?
I have a wealth of fairytale books in my bookcase, so I'll tell you what I know. There exist dozens of fairytale books, most of them modernized, with modern language, and modern versions of the tale. The most popular stories are reprinted again and again, and often adapted a lot. Many of the tales that we are all familiar with (thanks to Disney) are the altered versions of often much longer stories. A lot of fairytales have been toned down in their violence, or their message, over the years. There's been a lot of censorship, and now it is difficult to find the original version of any tale. The lesser known fairytales tend to be a lot more interesting in my opinion. They can sometimes be really bizarre.
Mystical creatures and monsters show up in countless fairytales, although animals (especially talking animals) are more common.
Dragons are rare in fairytales, despite how well known a creature they are in folklore.
Goblins appear occasionally, along with creatures such as
trolls, elves and fairies, which are all over fairytales. And when I say "elves", I do not mean the modern Tolkien elves. The word "elf" originally refers to magical forest creatures, often very small, and similar to fairies/fey. D&D borrows heavily from both fairytales and Tolkien, as well as pop culture.
With giants we at least have Jack and the Bean Stalk and with vampires you have Dracula -- but otherwise the best I can come up with is either from semi-recent literary history. I imagine medievel Europe has SOMETHING I should be reading for inspiration right? Like, is there not a classic story about hobgoblins or whatever?
Goblins, giants, brownies, fairies, those are all common fairytale creatures. They show up in dozens of stories. Jack and the Bean Stalk is but one of many. Jack features in other tales as well, some of which also feature giants.
The brave little tailor also runs into giants in one of his tales, and appears in several other tales as well, where he always tricks people in some clever way. Both are very similar stock characters.
Although it should be noted that fairytales often reuse the same name or stock character, for what might as well be an entirely different character. There's not a single connected universe between fairytales. But there are many tales that have giants in them.
I do not know many fairytales that feature a
hobgoblin specifically. The creature in Rumpelstiltskin has sometimes be referred to as a hobgoblin, but in the original tale I think he's simply referred to as either a dwarf, or an ugly little man. In the
Snow Queen there is mention of a hobgoblin, but I do not know if this is the original version of the tale.
Vampires are common in folklore and superstition, but not common in fairytales. Its bizarre just how many cultures on our planet have some sort of a vampire myth. If you are looking for a fairytale about a vampire though, you'll be very disappointed. There are few... perhaps even none.
(And they didn't all live in the forests either.) While precise usage would vary from region to region, the elf of folklore was a fairy and the fairy was an elf. And sometimes a dwarf. The word has Scandinavian origins, and there were dark elves and light elves in that country, though the description varied from region to region. The huldre, for instance, had cow tails, while the Danes thought they were hollow from behind. In Scotland, they tended to use elf to refer to larger, human size fey, but in England, it was more common to call the smaller fairies, males in particular, elves. 
