If the question was rephrased and lengthened, the answer could be "letters in this sentence". I can't think of a way of writing it that doesn't sound stupid, though.
Cliffy is right. It's elements (of the periodic table).
To begin with, 8 were found by a Swedish chemist named Karl Scheele (namely chlorine, flourine, manganese, barium, molybdenum, tungsten, nitrogen & oxygen). There are now 120 or so and more will probably be discovered.
Champagne, I thought Oxygen was discovered by Priestley. Scheele just arranged the known elements into their periods, according to what he thought were their numbers of electrons. He got a few wrong, if my memory serves me well, but he predicted quite a lot of other elements that had not yet been discovered, by looking at the gaps, and he also predicted what their properties would be. Clever chap.
Isn't it obviously, at the start there were 8 predictable answers to this question but by the end there will be around 120 including inane replies such as this one! But seriously, I'd have to agree with the "Periodic Table of Elements" reply. That sounds like the most reasonable answer.
However... Judging by my own reply it might relate to the number of typos expected in response to this question! (ie "Isn't is obviously, at the...") OK so I'm human, I admit it alright? Shet!!