I don't know if I have any truly rare vinyls, I have a number of limited edition colored vinyls that were released in very small runs, like Cloudkicker's Fade on Orange (100 copies), Scale the Summit's The Migration on Clear w/ Blue Haze (100 copies) and Gorguts' Colored Sands on Yellow in Red (150 copies). However I'm skeptical that these will have real collector value sometime in the future, or rather, that these albums will have significantly more collector value than just being a first press, since almost all of these I have are just a limited colored version in a much bigger vinyl run. Who knows though.
The only vinyl I have that I think actually has a shot of being rare one day isn't a metal album at all. It's my still sealed, first press deluxe edition of the first Run the Jewels album.