Tau Analyzer!

auCDtect Task Manager is a free GUI tool that lets you check if your lossless audio files were upconverted from a "lossy" file format.

Lossless Audio Checker is a utility to check whether a FLAC or WAVE file is truly lossless or not, by detecting cutoff frequencies. It can show you the full frequency range for each file.

Audiochecker is a tiny and portable tool which analyzes the source of WAV, LPAC, SHN, APE and FLAC audio formats, in order to verify if the encoding is lossless. If not, it means that the files in question are converted from other formats with lower quality, such as MP3.

Spectro is a freeware audio file analyzer for windows. Currently capable of reading FLAC, APE, MP3 and WAV files. Spectro lets you view vital data about compressed audio files and creates a spectrogram of the wave data. This allows you to quickly and easily spot quality issues with a file and also look for transcodes.