Zip2Fix is a portable tool which attempts to recover data from corrupt ZIP files.
It's very simple to use. Click Open, choose your broken archive, Zip2Fix recovers as many files as it can and saves the results to a new archive in the same folder (name.zip becomes name_ZFX.zip).
The program also displays its progress in a log, allowing you to see which files (if any) have been repaired, and which are still lost.
You can optionally save the log for later reference.
Zip2Fix would benefit from a few minor tweaks - like accepting files by drag and drop - but the core recovery engine works well. Grab a copy, you never know when you might need it.