This year's challenge was: Lego Atlantis
Fair enough, Lego has NO shortage of photo stock of their products. Even moreso, now that they've expanded to online and animated media. I acquired an underwater backdrop, complete with temple-ruins (he's really into Greco-Roman Architecture), some submersibles, and a pic of "Manta Warrior" - his favorite character from the series.
I threw these components into a Photoshop file and used Lego's website header - their font and design was just too good to try and reproduce by hand. Also, taking a tip from CakeWrecks, I decided to bake all the required text into the picture, rather than risk them writing something horrible in purple icing.
But, I wanted just one more element. I had done some marketing research with/on my son using the Lego Atlantis website. He'd picked out his favorite sets - one of which was a Seabed Scavenger - complete with giant claw, sawblade, and Manta Warrior. How difficult would it be to integrate this into the cake? Oh, about 30 minutes of assembly time...
So the night before, I rushed out to the local toy store, got the Scavenger, put it together, and hid it away - to be used as a cake-topper for the party. The sawblade would actually be embedded into the cake, as if they were mining for precious undersea resources, with the Manta Warrior standing guard.
Another successful party. The kids had a great time, and C. had no issues licking the frosting right off the sawblade.
The next thing my son wants: A Lady Gaga Jack-o-Lantern.