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. This handcrafted invitation is elegant and refined but needs to be done by a skilled calligrapher who may be difficult to find. You can also look for a printer who creates the look of calligraphy on printed invitations. Obviously, the printed calligraphy is more affordable than the hand_written calligraphy but may not be as elegant as the hand_written one.