Some people trash the dress. Others put it on eBay. If you are thinking of keeping your wedding gown to pass down to the younger generation, or if you want to get it in perfect shape for consignment, you will want to have your gown professionally cleaned and possibly preserved in an acid-free, archival container.
If you are just doing cleaning, your local dry cleaner may offer this service. Be sure to ask if it is done locally or sent out to a special service, and what is included. Gowns that will be stored for a long time should not be stored in plastic or vinyl which can come in contact with dress fabric and cause yellowing or discoloration. If a gown will be hung up, it's best to store it in unbleached muslin fabric.
If your gown will be stored for a long time, hanging it can cause the weight of the gown to pull on the seams and stretch the fabric, causing damage. It's best in this case to store it in an acid-free, archival-quality box.
At EJP Events / The Bridal Loft, we do offer this service not just to our own clients, but to anyone in Portland desiring cleaning and preservation of their gown. Simply call us at (503) 284-6756 or email email@example.com to make an appointment and we'll take care of you. Pricing starts at $165 for cleaning and box only. I've attached links to the order form for those who are interested in the details.
One more thing: no matter how you plan to have your dress cleaned, make sure to store it at room temperature and avoid places like attics, garages, and basements where temperature and moisture/humidity levels can fluctuate without your knowing. The top level of a closet in your house is a great spot.