Planting a garden in a keyboard. Best office prank idea, especially if the co-worker goes on vacation for a week or so. I would use a keyboard that looks like theirs though. That way you don't get into trouble for destroying someone's property.
Build-On Brick Mug -- Morning meetings suck. Make yours more exciting with the Build-On Brick Mug. It's a coffee mug that is compatible with LEGO& PixelBlocks, Mega Bloks, KRE-O, or K'NEX Bricks& and it's guaranteed to making your meeting better.
Lego cable holder - an awesome way to help you organize your cables! My husband loves lego crafts of all kinds & these lil guys are a great cable tidy for your home office. In need of more home office ideas? Check out this post