Makemake, outside the orbit of Pluto, is among other dwarf planets, specifically Eris and Haumea. The known dwarf planets join other large trans-Neptunian objects within the solar system.
The NASA New Horizons spacecraft, now slated for a rendezvous flyby of Pluto in the summer of 2015, will explore one or two ancient Kuiper Belt Objects (KBOs) in an planned extended mission. A KBO flyby is expected in 2018 or 2019, though it could be as early as 2016 or as late as 2021.
Since no other Kuiper Belt mission is planned - either by NASA or by any space agency - New Horizons is very likely to be the only spacecraft that will explore KBOs in the lifetime of most people alive today.