Religious Ceremony:
If you're getting married in a church or other house of worship, talk to your officiant and find out what is allowed in the sanctuary and what is negotiable. Some houses of worship will not let you play secular music/poetry or light a unity candle or have a handfasting, but some might.

Secular Ceremony:
If you're getting married in a garden, hotel, historic building, or other non-religious site, you have a lot more leeway in what you can include in your ceremony. If you have a religious officiant, you'll need to talk with him/her beforehand.

For the ultimate in a personalized ceremony, have a good friend or relative become a Universal Life Church minister (you can do it online even). The you can have that person read a ceremony that you write. ULC ministers can legally perform weddings throughout the US (a few states may have additional requirements).

Decorations:
Candlelight ceremonies are incredibly beautiful and look quite gothic. Make sure to check the fire codes of your wedding site first tho'!

Dark colored roses (such as a deep red) can make lovely decorations for any ceremony site. Dark ivy is another lovely touch. Calla lilies make a dramatic show (and they're sometimes associated with funerals too).

If you're getting married in a Jewish ceremony, you can make a rather gothic chuppah. Use black or dark colored velvet and trim it with dark fringe or braid. If you or someone you know is handy with a needle, you can decorate the chuppah with embroidery or quilting too.

Music:
Consider swirly, moody gothic music for your ceremony, or stick with dramatic classical works. Danny Elfman movie soundtracks (esp. Edward Scissorhands) can be very lovely too.

Photography:
The photo-journalistic style of wedding photography would probably be best to capture a gothic wedding on film. This style concentrates on telling the story of your day, instead of trying to force your wedding into a tired, traditional format.

If there are interesting historical buildings nearby (or your wedding location is historic), make sure to get pictures there. Marble columns, elaborate carved fireplaces, dramatic doorways, and the like can frame your wedding photos to great effect.

Definitely get some of your wedding pictures taken on black and white film. Black and white can add drama and depth to photos.