To inspire myself I just start messing around with materials and emitters. From there it typically blossoms into something that I personally couldn’t have ever imagined!
Majority of my time is spent running JangaFX, so playing with our software daily keeps me stocked with fresh ideas, though burnout is possible.
On the other end, I generally play a few games to get back into the VFX mood if necessary - Metro series, S.T.A.L.K.E.R series, Half Life series, etc. These games are generally toned for more realistic effects, but all have amazing atmospheres that get me back into the mood to make things.
Lastly, if I’m facing a pretty lengthy burnout I just get off my computer for a few days if possible. Take the weekend off and go hike or something along those lines. Then again, learning other skills on or off the computer is the another way to keep my creative side going, just not in the same area as VFX.