36" square for the neonatal unit at local hospital; 44 x 60 for most other charity needs. I also make a few for 'men' that are larger, 48 x 72. Those usually go to someone in the church who is ill or going through difficulties.
Really, just about any size is going to be needed and loved. My church group makes them for 'Camp Reach For The Stars,' for kids with cancer. My guild's philanthropic group makes and donates about 650 a year to over 15 recipient groups, we've never had a complaint about size yet!
Almost all the quilts I make are donated, and the largest benefit of this is to me, it is improving my skills! Also, I don't have to worry much if a quilt doesn't come out as I hoped; even as I learn something from it, that quilt will be appreciated anyway!