We had the best LEGO birthday party for our 7-year-old son, and for pretty cheap. First of all, the INVITATIONS went out.  I used large Megablocks (huge sized plastic Lego-looking pieces that I got at a yard sale) and formed them into cubes.  I printed the information using Lego fonts (free online at many locations), glued the paper to the cubes, and then cut them apart with an exacto knife. Then, I put them in large clear bags with a tag that said: This birthday invite is a mystery! Just put the LEGO's together and see! (Child's name) We hope you can come help us BUILD some fun together!". The guests had to assemble the blocks to discover what the message read. They were a huge hit.  For DECORATIONS I just used red blue and yellow streamers and balloons...the classic LEGO colors. ACTIVITIES: When the guests arrived they began building with Legos. I had dumped them all into a small blow-up swimming pool to keep them contained.  GAMES: Once all of the guests arrived we played Lego Pictionary. I had printed out several cards with simple pictures of common objects on them (car robot a square a boat etc). The kids each picked a card and built that object. Then the other kids tried to guess what they had built. They loved doing that. Then we had a speed building competition where everyone had 2 minutes to build a car and we voted on who's was best.  Next everyone picked a LEGO minifigure to compete with.  We went outside in our backyard where I had a LEGO obstacle course set up.....1.)Lego guy goes through wrapping paper tube 2.) rides on train set from one end to the other 3.) travels by Barbie car to end of yard 4.) rides on boat across baby swimming pool 5.) rides on a spoon to other end of yard 6.) rides in bucket down zip line created with rope 7.) gets catapulted in a butterfly net 8.) flies in a paper airplane and 9.) crosses a finish line.  The kids loved this and competed for who could complete it in the fastest time. Then we went back inside and the kids had 1 minute to get as many LEGOs out of a glass full of Jell-0 that they could (I put about 20 LEGOs per cup including swords minifigure body parts and just LEGOS). Then we had CAKE: I used mini-loaf pans and baked 12 mini loaf cakes. I frosted each in a primary color (used blue red and yellow) and then used the same color M&M's for the knobs. They looked just like LEGO bricks. I piled them up randomly to look like a LEGO pile on a tray. Each kid got their own cake to eat. After opening presents each child got to take home a goodie bag. I went to the LEGO store and asked them for some of the little bags they use for merchandise (they are yellow and say LEGO on them)....they gave them to me for free. They also had free LEGO club magazines. For the FAVORS I put in a notepad that I made (I used yellow foam and cut out it out in the shape of a LEGO minifigure head and drew a face on it with marker...looked just like a LEGO head) and stapled it to a few sheets of paper and trimmed them to be in the shape of the head) LEGO crayons (I used a LEGO minifigure ice cube tray and melted chopped crayon bits and they created crayons shaped like LEGO guys) the LEGO club magazines and LEGO candy bars (I took Hershey mini candy bars and wrapped them in my own wrappers. You can print off a picture of a lego blown up to the size of your candy bar and wrap them...once all wrapped and in a little baggie they looked like a bag of LEGOs....turned out really cute!).  It was a fun party and the kids had a great time! "