I include this piece in the interest of completeness. I have played it by request at a wedding - and it would fit a gothic theme.
Full Title Toccata in d minor BWV 565 by Johann Sebastian Bach (1685-1750)
Notes The opening movement of the much longer Toccata and Fugue in d minor BWV 565, this is probably the most famous piece of organ music. It is not especially suitable for most weddings. Rather intriguingly, this most famous piece of organ music by J S Bach is now though to be not originally by Bach, not for the organ (but for the violin) and not in d minor. It's still a great piece, though.
Duration Approx 3 min
- Organ alone
- Piano alone
Source of printed music widely available, for example in the free edition by Pierre Gouin on IMSLP