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.
Many times, traditional afternoon weddings, followed by evening dinners and receptions do well with the classic wedding invitation. However, weddings that are in the morning, with afternoon receptions, or weddings that are in the early evening with late night receptions are ceremonies that might benefit from a different type of wedding invitation. You have to use your best judgment and ask yourself if a traditional wedding invitation is really the best style for your ceremony.