My son LOVES LEGO so it seemed the perfect birthday party theme. But I was concerned that not all his friends shared that interest, but I knew they all love playing good guy vs. bad guy. So I got some great ideas from this sight and added to them. We decided to make it a LEGO Agent party after his favorite LEGO series. For each invitation we used 5 old Duplo blocks put together in a square. We wrote the information on them in permanent marker, then took them apart and put them in an envelope and hand delivered them. The boys had to reassemble them in the right way to find out the information about the party. They loved this, so we were off to a good start. We decorated the dining room in primary colors - red table cloth, blue plates,yellow naplins -  and put hand drawn pictures of large Lego bricks around the room. We used some of my sons Lego creations as a center piece and hung some from the light over the table. We also made Lego placemats. The background was Lego scrapbook paper I bought off e-bay, the main picture was a Lego airplane my son cut from a Lego magazine. The jet stream behind the plane was made up of Lego facts we got off the internet and typed up. We made one placemat and color copied the rest. I didn't laminate them because of the cost.  On the day of the party as the boys arrived they received a homemade cardboard name tag that hung from yarn around their necks. On the name tag it said Agent ... or Evil ....,with their names, and had a picture of a LEGO Agent figure (good guy or bad guy) that my son had cut out from a LEGO box and taped on it. They played out these roles later in the party. The first activity was coloring LEGO coloring pages printed from the LEGO web site and decorating a treat bag that went along with them throughout the party. After all the boys arrived and finished coloring they were told there was a Duplo block hidden in the room. They needed to find it and we would read them the riddle written on the block. They had to figure out the riddle to know where to go for the next activity. There also were small prizes for each of them hidden near the Duplo block. (Prizes were fruit snacks, sports stickers - 3 kinds, punching ball, activity pad.)They did 6 activities - coloring, Lego creation building with 20 blocks, a running game to disassemble their LEGO creation, drop the LEGO in the milk jug, pin the bump on the LEGO brick, cake and ice cream. After each activity they found a Duplo block with a riddle and small prizes. (We made sure each boy found one of the Duplo blocks with the riddle.)The riddle they found after eating cake (two Lego Brick cakes made from a frosted pound cakes)lead them to their big treat bag prize, a Lego Racer kit for each of them that we got on sale from the Lego web site. Then they were told to assemble all the Duplo blocks they had found so that on the back sides they made one large final clue that lead them into the play area where they had time to play Lego Agents vs. Evil guys. I love working with large cardboard appliance boxes and had painted a replica of the Lego Agent Volcano Base (a standing up refrigerator box) for the bad guys base, and the Lego Agents Mobile Command Center (a lying down refrigerator box) for the good guys base. They didn't have a lot of detail, just windows and doors, but the boys enjoyed just being able to play. Too soon it was time to go. The parents told me for a couple weeks afterward that the kids had a great time and kept talking about the party. My son helped with a lot of the planning and preparations and that time together, and a happy birthday boy, are what I love.