LaTeX is just about the easiest way to write anything that's meant to go on the printed page eventually. The labbook style by Frank Kuster makes this very easy. The style is included in MikTeX and Texlive already.
The style defines three major new commands: labday, experiment, and subexperiment, which you use in place of chapter, section, and subsection. The documentation that comes with the package is very clear, and provides several example files.
LyX is a frontend for LaTeX that hides all the issues of importing data, putting figures in, and not making typos in the commands and environments. To use it with the labbook LaTeX style, you will need this layout file.
I recommend using \frontmatter before the title, table of contents, etc., and \mainmatter before the first actual entry. That way you won't have to renumber pages in the lab book as your table of contents gets longer, because the title and table of contents will be numbered with Roman numerals, and the first page of content will start again with an Arabic 1.