\documentclass{article}
\usepackage{tikz-timing}
\newcommand{\degr}{degr}
\begin{document}
\begin{tikztimingtable}
Clock 128\,MHz 0\degr & H 12{2C} G \\ % ends with edge
\color{red}\tiny Clock 128\,MHz 90\degr & [C] 12{2C} C \\ % starts with edge
Clock 128\,MHz 180\degr & C 12{2C} G \\ % ends with edge
Clock 128\,MHz 270\degr & 12{2C} C \\
\end{tikztimingtable}
\end{document}
I'd like all labels 'Clock...' to be left aligned.

node-familieslibrary, it is also possible to saytiming/name/.append style={Text Width=timing, align=left}after all rows has been added totikztimingtableenvironment. (The implementation ofText Widthis not perfect.) – Qrrbrbirlbel Oct 26 '13 at 04:54