I will state up front that I know I'm at risk of quality loss. Let's assume I'm fine with that.

Is there Windows software out there that can re-encode MP3 to MP3 at a lower bitrate (hopefully in batch mode) and preserve the ID3 tags?

I've ripped hundreds of CDs using EAC and LAME (alt preset extreme). I have an ipod on the way and want to re-encode down to 128 or 160 kbps so I'm not out of space before I even load it. I know it's possible to re-encode with RazorLame, but the tags get blasted away.

The software of choice is foobar2000.

Try transcoding to "lame --vbr-new -V5" (~130kbps) and verify if your iPod plays the resulting files without problems.

Foobar2000 is an excellent choice. You may also try dBPowerAMP Music Converter (dMC) ---> Link

Thanks, Egor and audiomars. Foobar does exactly what I want!

Another way is, your Ipod itself will down convert the songs to 128kbps AAC automatically (If you choose it) as you add songs, that way keeping your original files on your computer and saving space on your ipod

There's one problem with foobar2000 and iTunes/iPod: foobar2000 uses ID3v2.4 tags but the Apple software uses ID3v2.3. For the exact reasons you can search a little bit in the hosted fb2k forum...

But to make things easier for you might want to convert the ID3v2.4 tags to ID3v2.3. MP3Tag is able to do that easily (set the "save tag" in the options accordingly).

Lettting the iPod do the conversion is probably the easiest way and there won't be any trouble with ID3v2, but maybe you get better sounding result with lame -V5 and decide to better use lame for the transcoding. Therefore keep the problem with the tags in mind.