Through Pinterest I found the blog Delia Creates (deliacreates.blogspot.com), which had so many wonderful ideas and some free printables. Here's a link to her main post about her son's party, which has links to other posts at the bottom.
Invitations
I posted earlier about the pictures we took for the LEGO Birthday invitation. Here's what I ended up putting together. The center picture was a free image available on Delia Creates, here. I used picmonkey.com to create the photo collage and add the text. (I enjoy that the site makes it easy to download your final image so you can print locally.)
The LEGO Cake
We had lots of fun making the LEGO cake (yes, I do mean "we"... my wonderful husband helps with the birthday cake process. He has a much better eye than I do for cutting cakes to shape and adding fun details, like all the mischievous characters above). The blocks are made from cake baked in mini loaf pans, trimmed to be smooth rectangles. Each "bump" is half of a regular sized marshmallow. We found frozen marshmallows (like cakes) are easier to frost. Toothpicks were helpful to create handles in the marshmallows and sometimes to keep in the place on the blocks. The frosting is just regular frosting from a can. My husband created the great colors (have I told you I wouldn't attempt a birthday cake without him?). I know this isn't the clearest picture, but underneath the plastic wrap is paper with "bumps" printed on it, again from the Delia Creates link above. My son loved seeing all the characters on the cake but was most concerned with the one near the bottom as it appears his legs are stuck in the cake (really his legs were missing and that was Dad's solution!).
A Fun Favor -- Lego Crayons
We recycled old, broken crayons into a Lego mold I ordered from Amazon (Building Bricks Ice Cube Tray or Candy Mold
I put the crayons in paper Lego boxes (also from Delia Creates) to give to the kids at the party.
Activities
I printed LEGO person color sheets for the kids to color.
My husband and I enlarged a picture of a LEGO person onto a poster, which became a "pin the head on the Lego person game". I laminated the head so that I could use glue dots and not worry about it ripping each time.
Of course after presents were opened, putting new LEGO sets together became a default activity. We also got out our larger Mega Blocks for a few younger guests.
There were a few other Lego details we did that were fun -- a present wrapped like a Lego and a birthday sign with the number 4 made from legos.
If you're planning a Lego party in the near future, I hope you have as much fun as I did with the process. The theme was a hit at our house on the gravelly road :)