Quick, good way to normalise a batch of too-quiet MP3s. Sounds obvious, I use it all the time!
1.) Get a blank CD.
2.) Select a CD's worth of MP3s you want to normalise.
3.) Record them as an ordinary audio CD with Windows Media Player (Itunes works as well, Mac users!)
4.) Because both the above normalise automatically when recording CD's, you end up with a CD of perfectly normalised tracks!
5.) Rip the CD you've just made back to the hard drive. You now have a collection of perfectly normalised tracks for the price of a blank CD.
Of course, if you're normalising a thousand MP3s or so that could get a little pricey, so if anyone knows how to make ITUNES/WMP save the completed tracks to hard drive instead of to CD, feel free to say - I don't know how to do that. But the above works.