Given my interest in Voigtlander lenses, I decided to make a list with the best reviews I find and it only makes sense to share it. I will be concentrating mainly on tests done with Sony cameras and will be updating this post over time.
15mm f4.5 Heliar III (M-mount)
Review from Ian Norman at Photoncollective - with great landscape samples
Review from Ian Norman at Lonelyspeck - astrophotography
21mm f1.8 Ultron (M-mount)
Review on 3DKraft - a comparison of various wide angles
35mm f1.7 Ultron (M-mount)
Review by Phillip Reeve - plenty of samples