The My Year in Temperatures scarf grabbed my attention immediately. You assign a yarn color to a temperature range. I decided to go with a rainbow-ish theme, so a temperature above 90 F is red, 85-89 is red-orange, 80-84 is orange, and continues in 5 degree blocks down to 20 or less as dark gray. This should cover the temperatures in Atlanta over a year. Every day, you note what the high temperature is and knit two rows of that color on your scarf. I'm planning on doing a k2 tog-yo row on the last day of each month as a divider. I'm using fingering yarn and doing this as a stashbuster project.
The My Favorite Things scarf is another idea that sounds fun. You gather up all your favorite motifs and knit them into a single thing. The original is done as an infinity scarf. I'm thinking about using them in a different way, maybe a pillow. It's a way of revisiting favorite designs or even trying out new ones. If it's a favorite, there probably is leftover yarn that can be used to make it, too.