For my son's 8th birthday we had an alien party. We made alien invitations on the computer, complete with an alien menu that really piqued the kid's interest. We served "Flying Saucer Pizza" (individual pizza's), "Extraterrestrial Nachos" (the cheese was tinted a bright green - the boy's loved the gross out factor of green cheese!), "Alien Brain Freeze" (a green Kool-Aid sherbet)"Martian Cake" (pistachio cake with green whipped cream icing) and "Outer Space Punch" (a frothy green sherbet fruit punch).  I painted the light bulbs over the kitchen table with a green acrylic paint to give the room an eerie green glow and we had alien themed partyware.  Glow in the dark stars and and alien spaceship were also hung from the ceiling. Towards the end of the meal, my son was delivered a letter that began "Greetings Earthling Alex...." that I had created on the computer. I used a bizarre font to write the letter from the "aliens" and the kids were told the names of the aliens and their planet, the mission they had come on, and the special alien spaceship treat drop they had made in the field across from our house.  The kids excitedly grabbed empty treat bags and went on a treat hunt in the field to find all kinds of candy and a special alien egg (one for each child, as explained in the letter). We hid all sorts of individually wrapped candy, including things like gummy alien eyes (my son's birthday is around Halloween, so some neat things for this theme are easy to find!) Each egg contained a piece of glow-in-the dark rock from the aliens planet and length of alien antennae (glow-in-the dark elastic string that they could wear around their necks) and a miniature green alien.  I bought all of these at a large craft store. After the treat hunt, we opened gifts, while listening to a silly C.D. that included songs like "Flying Purple People Eater" and "The Monster Mash". We ended the party with a Mad-Lib type Alien story that I had created, where the kids were asked to give words to fill in the blanks to make the story wild and outrageously funny (at least to them it was!) I usually try to plan parties that last about 1 1/2 hours, and with the meal, it filled this time just about right.