Samplephonics have released a collection of 33 free reverse sound FX samples.
The collection is available for all their registered users, the registration being free, of course. I strongly recommend you to register at Samplephonics, because you will have access to all freebies, including ethnic or unusual instruments, processed drums or sound effects. For example, I like very much their SFZ instruments, in particular Shakuhachi and The Wizard of Mbira.
The current freebie, 33 Free Reverse FX, is useful to create risers, builds, tension and, why not, sound design- if you like to sample and further process the sounds.
For easy handling, it comes with sampler instruments for Halion, Maschine, Kontakt, ESX24, MachFive, Ableton Sampler and Reason NNXT. The individual samples are delivered as 24-bit WAV files.
All included sounds are 100% royalty free.