I had two stacked 125s but it was a steel stand and didn't look great. I think datnoid101 had a couple stacked 125s is his "redoing the datnoid room" thread, with a DIY stand... they looked nice to me.
I have seen stacked 125's at LFS. They are tube steel. I have made a stand for dual 90's, but it was nothing fancy and kept in a basement. Perfecto used to make a steel 125 stand that holds dual 30 gallon breeders (30x18) under the 125.
I really like the looks of 12 Volt Man's, but it doesn't look like there is any room to work on the 50.