I'm a big fan of IMSLP and have been using it for a while now. I love that I have one non-profit place that I can find most scores I need. I don't have scores to contribute myself, but since my forte is computer graphics and automation, I thought I'd offer help with creating PDFs.
So, if you need raw scans processed, PDFs corrected or redone, pages deskewed, scans compressed, etc., I'd be happy to do it for you. I have all the computer stuff that's needed (Acrobat, ImageMagick, etc.). Just PM or email me.