I know that the Voyager missions were launched years ago, and are quite a long way out there.
With the problem of communications taking forever to get to the probe and back, what are we currently doing with the probes for science?
The two Voyager spacecraft are now conducting the Voyager Interstellar Mission:
The mission objective of the Voyager Interstellar Mission (VIM) is to extend the NASA exploration of the solar system beyond the neighborhood of the outer planets to the outer limits of the Sun's sphere of influence, and possibly beyond. This extended mission is continuing to characterize the outer solar system environment and search for the heliopause boundary, the outer limits of the Sun's magnetic field and outward flow of the solar wind. Penetration of the heliopause boundary between the solar wind and the interstellar medium will allow measurements to be made of the interstellar fields, particles and waves unaffected by the solar wind.
Recently it was announced that Voyager 1 had in fact entered interstellar space on August 25, 2012. The heliopause boundary was sharp, going from lower to higher density plasma and a change in the direction of the magnetic field (though a smaller change than expected). However it took a year to figure that out, waiting for the assistance of our Sun with a coronal mass ejection that excited the local plasmas, and the interpretation of that data.
Voyager 2 has not reached interstellar space yet, but it is expected to while it is still operational.
The Voyagers should remain scientifically operational through 2020, with continued operations with reduced science possibly as far as 2025.
From what I understand, the probes are at the end of their lives; their nuclear fuel is almost out and power is limited to run just a few systems. As for the science, they are just reporting on the conditions of deep space. The Voyagers lasted longer than even it's designers thought it would. http://voyager.jpl.nasa.gov/news/factsheet.html
The probes instruments are: infrared, ultraviolet, magnetometers, plasma detectors, cosmic-ray and charged-particle sensors. They report on the light, magnetism, and radiation of deep space.
The Voyager probes are currently further away from earth than any object before. Knowing their position alone gives interesting scientific data, because it tells us their speed and direction, which gives us information about the forces which act on objects so far outside of the solar system (microgravity, acceleration through solar winds, friction with particles in interstellar space...).
But there are also some scientific sensors on board of the Voyager probes which still give interesting data
Most instruments on board of the Voyager probes were designed for observing the planets and their moons during the fly-by's (optical cameras, infrared spectrometer etc). These instruments haven't got many applications in open space, so they are powered down.
But there are other instrument which are still active and give very interesting readings of the heliosphere, the area where solar winds interact with interstellar space. Most of what we know and are still learning about this area of space is from these instruments on the Voyager probes:
The Voyager probes are currently planned to continue their mission until 2025 when their RTGs will become too weak to still supply these last instruments.