Is there a "high temperature" variant of 0 degrees Kelvin? I know that -273.15 degrees celsius, also known as Absolute Zero or 0K is the low temperature limit for objects, but is it possible that there is a 'highest temperature?'
I would have to guess that it's when it allows objects to reach light speed, but I believe there has to be some 'set temperature' that is the limit for anything. Am I wrong or is there an actual answer?
 A: There is a "high temperature" limit, it is actually the same point.  5K is hotter than 1K, and 1000K is hotter than both.  The temperature $\pm \infty$ is actually the same temperature, and for negative temperatures you get hotter the closer you get to zero (from below).
Most systems cannot reach negative temperatures, but even if you can you can't get all the way to zero from either direction.
If this seems weird, note that $$\frac{1}{kT}=\frac{d S}{d E},$$
So if giving a little bit of energy $E$ gives a large increase in entropy $S$, then $1/kT$ is large (and positive), so $T$ is small (and positive).  If a little bit of energy gives no change in entropy (not possible for most systems) then $1/kT$is zero, so $T=\pm\infty$.  If a little bit of energy  gives a large decrease in entropy $S$, then $1/kT$ is large (and negative), so $T$ is small (and negative).
These changes in entropy can never be infinite because entropy is a real and finite thing and we don't make vanishingly small changes in energy, so there is no infinite rate $\frac{d S}{d E}$. And that's why temperature is never zero.
edit to discuss when negative temperatures can occur
All you need for negative energy is that the range of small-and-practically-accessible energy exchanges can only cause the entropy to get smaller when it accepts energy.  This makes it statistically favorable to give energy to positive temperature things (then both entropies can go up), so it is hotter than all of them (so negative temperature is hotter than positive temperature).  This might not be because the negative temperature system has components with a strict maximum energy, just that those higher entropy states are not accessible.  For instance if your collection of two state systems don't have enough kinetic energy to combine to create electron-positron pairs it doesn't matter that with a large amount of additional energy they could increase their entropy by doing so, as long as that isn't going to happen.  Statistical physics is about what will happen on time scales long enough for quasi-equilibrium to occur.
