We had friends that are having their third child. They have one of each so far. They had the little boy drinking a blue soda and the little girl drinking a pink soda, then the next picture was of the little girls soda all gone with her making a sad face and the little boy holding his blue soda proudly. The picture was captioned "It's a..." and "boy" was the first comment. You could do you and your DH drinking the correct color soda.
For my friend we made little onesies that said "grandma's lil lady" and "grandpa's dance partner" they were super cute and since they found out close to Christmas they had their parents unwrap the presents last.
With our oldest we sent out little boxes of pink candies with a note at the bottom of the box saying "congrats on your first granddaughter"
I'm doing mine via photos. I don't know if these have been suggested already but one of the ones I did was put blue balloons in a wooden box that we had and my husband and I stood behind it while our 2 and 4 year old daughters opened it. I taped the strings of the balloons to the bottom so they wouldn't float away just in case the photographer missed the balloons coming out and needed to have us do it again. Lol! I also got on my knees so that I was the same height as my kids and the three of us showed our bellies (mine was a side view though-lol) and we each had a letter painted on our tummies so that we spelled out "BOY." The last thing we did was that on the side of my tummy I took a baby doll and painted its foot with blue paint and put a tiny blue baby footprint on the side of my stomach. Then my husband put his arms around my stomach and with his hands made a heart around the footprint. :-) After the photo session I also thought that I could have taken 5 blue balloons and put a letter on each one to spell out "Isaac" (our baby's name) and had us all stand in a row while holding the balloons in order. :-)
I know a girl who had the dr write it on a paper, and put it in a sealed envelope. She gave it to her best friend and her friend set up the final decor for the gender reveal party. To find out she took black squirt bottles and filled them with blue paint. The parents got to find out in front of everyone by squirting the paint on a onsie hanging on the wall!