HTC One (M7 / CDMA)
Original Clock in Sense 5.0
Google: "HTC weather widget apk" and download the apk. Install app installer free (or any other free apk installer app from the play store), run, install the apk and voilà!.
An advice: try to download the one from the Droid DNA, you can re-size one from older HTCs but it will look odd.
I also miss the old HTC clock/weather widget. The one on my old Inspire 4g, Amaze, one X... It will for sure look cool on the HTC one, I guess that It'll somehow mess a little bit with the new home screen functionality.