Pioneer 10, Pioneer 11, and the two Voyagers are all headed out of the solar system. Has anybody extrapolated where they will all end up (if at all)? Is there a graphic that depicts the direction of flight of all four spacecraft?
Besides "beyond the heliopause", they are not ultimately headed towards anything in particular. The sparsity of the universe and even our galaxy means that they are unlikely to encounter much of anything without being specifically targeted for it (which is out of the question at this point).
This paper addresses this question more specifically (for Pioneer 10 and 11, at least). It states that Pioneer 10 is headed in the general direction of the star Aldebaran (part of the Taurus constellation) (which it will "reach" in about 2 million years), and Pioneer 11 "should pass close to the nearest star in the constellation Aquila in about 4 million years".
As far as the Voyagers:
Voyager 1 will drift within 1.6 light-years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis which is heading toward the constellation Ophiuchus. In about 40,000 years, Voyager 2 will pass 1.7 light-years (9.7 trillion miles) from the star Ross 248 and in about 296,000 years, it will pass 4.3 light-years (25 trillion miles) from Sirius, the brightest star in the sky . The Voyagers are destined—perhaps eternally—to wander the Milky Way.
This page gives a nice overview of the relative positions of these probes as of 2011:
Voyager 1 is the most distant spacecraft, about 17.5 billion kilometers (10.9 billion miles) away from the sun at a northward angle. Pioneer 10, the next most distant, is about 15.4 billion kilometers (9.6 billion miles) away from the sun on the opposite side of the solar system. Voyager 2 is about 14.2 billion kilometers (8.8 billion miles) away from the sun on a southward trajectory, on the same side of the solar system as Voyager 1. Pioneer 11 is about 12.4 billion kilometers (7.8 billion miles) away from the sun.
Heavens Above has a slightly better graphic, IMO:
Here is a helpful image I received from Dr Lasher from one of his AIAA astrodynamics papers from the 1970's it reflects the Jupiter aim points for the Star 37E after separation from the Centaur upper stage for the pioneer spacecraft.
The B plane of a planet is always changing do to spacecraft incoming speed and line of flight(geometry) and epoch(time) notice the upper stage did not do such a good job with Pioneer 11 so Pioneer 11 had to do a TCM-1 to move the spacecraft over to the Hyperbolic circle on the right.so in this case the pioneer 11 Star 37E solid upper stage is in a heliocentric orbit while Pioneer 11 went to a Saturn flyby into interstellor space.