Saw a guy with big calves at my gym doing these... a year ago he didn't have big calves.
Squat rack, 2 45's side by side on the ground. Guy had the bar on his back loaded up with some plates, stepped halfway onto the 45's (so that his heels were touching the ground, but his calf was being stretched), and essentially did free weight standing calf raises. I've been doing these, and I gotta say i feel they much more effective than their machine counterparts, and I've noticed some growth. Just wanted to share.