Aurebesh  |  Klingon  |  Kot  |  Láadan  |  Lincos  |  Mando’a  |  Mirad  |  Na'vi  |  Quenya & Sindarin  |  Ro  |  Solresol  |  Toki Pona  |  Tsolyáni  |  Vampirese  |  Wardwesân
Amellaibian  |  Belter  |  Dothraki & Valyrian  |  Enochian  |  Esperanto  |  Hawaiian Pidgin  |  Ido  |  Interlingua  |  Latino sin Flexione  |  Lingua Ignota  |  Loglan  |  Sudric
Codex Seraphinianus  |  The Voynich Manuscript  |
A priori languages are invented from scratch, a posteriori languages are those built on an existing language or combination of languages. Of all the above Toki Pona is one of the most recent, invented by Sonja Elen Kisa, a 28 year-old Toronto translator, to help herself out of depression; also Wardwesân, a massive conlanguage project created by a pseudonymous French author.
It's notable that five of the above a priori languages come from science fiction and fantasy. I've already read Suzette Haden Elgin's radically feminist Native Tongue which first introduced Láadan, and I have somewhere M.A.R. Barker's Man of Gold, set in his world of Tekumel and which features the language Tsolyáni, and is by all accounts a very detailed piece of worldbuilding.
The wiki-site Langmaker, which I only looked at a few times before it disappeared in January 2008, claimed there are 1,902 artificial languages in the world, and I'm sure there are quite a few in online gaming.
Are Elvish, Klingon, Dothraki and Na-Vi real languages?
Top 10 Invented Languages