The yaoi pairing of Captain Kirk and Commander Spock, from Star Trek. Widely considered canon.
Most Spirk fanfics are either pointless fluff, or insanely dirty sex scenes with no plot whatsoever. If you find a good fanfic that has an actual plot and isn't pointless fluff, good for you!
Many people consider Spirk to be canon, because of the Backrub Scene in the TOS episode, Shore Leave.