For the 301 / 401 machines:
http://shop.sew-classic.com/Singer-S...oot-384037.htm
http://shop.sew-classic.com/Singer-S...KED-P60417.htm - This is the one I mentioned in a previous post.
For the low shank machines, Leah Day recommends this one:
http://shop.sew-classic.com/Low-Shan...td-SCF4021.htm - with modifications, she talks about them and has a video on her site. I have the foot here, but haven't made the modification yet.
http://shop.sew-classic.com/Low-Shan...-SCF4021-L.htm - I've used this one as is, it's my "go to foot" for the low shanks. I like it better than the plastic ones, especially the ones that have the plastic mount on them. Those seem to loosen and I have to retighten periodically, and have actually had them fall off while stitching.
And as everyone mentioned, yes, the 15 is better still than the 301 for FMQ. The bigger harp especially is nice. I completed my first quilt using one.