Since Sentinels of the Heliosphere in 2008, there have been a few new missions, and a few missions have been shut down. As of Fall of 2012, here's a tour of the NASA Near-Earth Heliophysics fleet, covering the space from near-Earth orbit out to the orbit of the Moon. Revision (November 9, 2012): The RBSP mission has been renamed the Van Allen Probes. NASA Press Release.
The satellite orbits are color coded for their observing program:
Magenta: TIM (Thermosphere, Ionosphere, Mesosphere) observations
Yellow: solar observations and imagery
Cyan: Geospace and magnetosphere
Violet: Heliospheric observations
Hinode: Observes the Sun in multiple wavelengths up to x-rays. SVS page
IBEX: The Interstellar Boundary Explorer measures the flux of neutral atoms from the heliopause.
Lunar Orbiting Fleet
ARTEMIS: Two of the THEMIS satellites were moved into lunar orbit to study the interaction of the Earth's magnetosphere with the Moon.
Note: A number of near-Earth missions had their orbits generated from Two-Line orbital elements valid in July 2012. Orbit perturbations since then may result in significant deviation from the actual satellite position for the time frame of this visualization.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 220.127.116.11.0