Perhaps there is a hobby that both of you love to do. You can use this 'theme' in your wedding invitations as well. If you both love to fish, you could use fishing line and lures for your invitations, or a hobby of wood_working could provide you with a way to expand your hobby into creating some special invitations. Regardless, if there is a hobby that the two of you share that helps to define you as a couple, don't be afraid to use it to your advantage and choose the best part of your hobby to direct your unique wedding invitation choices.
Calligraphy. Calligraphed invitations are very elegant. They work well for weddings with an old fashioned theme, but can be very expensive due to the amount of time and effort involved in producing them. Because of the expense, you might also look for a printer who creates the look of calligraphy on printed invitations. Note: When deciding on whether to choose calligraphy invitations, remember that you need to allow extra time for preparation. Keep in mind, too, that this type of invitation may smudge if it comes in contact with moisture.