Whether it's for a wedding or for an event, I also suggest starting with thinking about the overall theme and 'feel' of the event.
The term 'out of the box' is overused these days, but I like to use it literally when thinking about gifts for guests--it's time to give out something that cannot fit in a box. Let me give you an example:
A recently married couple, whose wedding theme was 'Evergreen', gave out small Evergreen trees that could be planted and that could grow alongside their marriage. This was relatively inexpensive and a wonderful way to bring the theme of the wedding together.
How about an example from the Corporate World:
A company celebrating a successful quarter wanted to give back to their employees and special clients. The company gave out high-end bottles of champagne with two champagne glasses--so the 'Celebration' could continue at home.
The world of gifts has moved way beyond chocolate truffles and personalized wedding coasters-embrace the options!