Batch audio processing I use Peak. Else to normalise a batch of similar tunes together: To normalise an album or group of songs of similar stature I'd put them into Toast, create an audio disk image & open that with Peak (Designer II element reading.) Then normalise it to the % of what is best suited for the end cause. Then extract the tunes individually using Toast or jam.

For windows, I'm not sure of a "free" batch normaliser but I'm sure they're out there. I like peak because I can normalise at a % of maximum such as 70 or 80%. Normalising % for me not only depends on type of content & target media, but also quality of source.