My son is 8 months old. Each month on his "month birthday" I create a sign that says "I'm (blank) months old. I then take pictures of him with the sign. I also try to plan a theme for the signs around current milestones or holidays. Example: For January, I took a picture of him in just his diaper with a new years hat and horn (aka. baby new year) Previous milestone pictures have been sitting up, and standing/cruising. February will be cupid, March-shamrock glasses from the dollar store and April and be bunny ears.
Another project I have planned (though haven't started yet) is his baby scrapbook. I am planning a "song/music" theme for it. (My husband is a band director and we met in college band) I will use various songs to create themes/phrases for pages. Ex. Beautiful Boy by John Lennon for newborn pics. Rubber Ducky (from sesame street) for 1st bath pics, Baby Mine (from Dumbo) for sleeping pics.