One thing that makes any type of party special is providing people with a unique invitation to your event. The best way to do this is to personalize it with a name, age, or theme. My favorite place to find invitations is through Etsy (http://www.etsy.com/). I have used several different vendors in the past and have had wonderful experiences with everyone; the best thing is that you will receive a file with your invitation and you can then choose to print them out or send them through email. This is a very easy and inexpensive way to personalize your event.
These are two of my favorite shops that have great products and wonderful customer service: