A quick automatic tagger for MP3 (uses eyeD3 - http://eyed3.nicfit.net)

masstagger.sh

#!/bin/bash

# This expects files ordered like:
# Artist/Album/01 Track Title.mp3
#
# You should provide the dir containing the Artist dirs at the command line.

START="$1"

if [ "$START" == "" ]; then
  echo "You must tell me where to start."
  exit 1
fi

cd "$START"

for ARTIST in *; do
  if [ "$ARTIST" == "VA" ]; then
    # Avoids albums by Various Artists
    continue
  fi
  cd "$ARTIST"
  for ALBUM in *; do
    cd "$ALBUM"
    if [ "$(ls *.mp3)" == "" ]; then
      # Skips empty dirs/non-mp3 files (for now)
      cd ..
      continue
    fi
    for FILE in *.mp3; do
      TRACK=$(echo "$FILE" | egrep -o ^[0-9]{2})
      SONG=$(echo "$FILE" | sed s/^[0-9][0-9]\ // | sed s/\.mp3$//)
      # Workaround for eyeD3 bug with UTF8 chars
      eyeD3 --to-v2.4 "$FILE"
      # DO IT!
      eyeD3 --to-v2.4 --set-encoding=utf8 \
        --artist "$ARTIST" \
        --album "$ALBUM" \
        --title "$SONG" \
        --track $TRACK "$FILE" || exit 1 
    done
    cd ..
  done
  cd ..
done

vatagger.sh

#!/bin/bash

# Same as masstagger, but for albums by Various Artists
# Differences: uses one less directory level and detects artists/titles differently.
#
# Expects files like:
# VA/Album/01 Artist Name - Track Title.mp3
#
# You should provide the "VA" dir at the command line.

START="$1"

if [ "$START" == "" ]; then
  echo "You must tell me where to start."
  exit 1
fi

cd "$START"

for ALBUM in *; do
  cd "$ALBUM"
  if [ "$(ls *.mp3)" == "" ]; then
    # Skips empty dirs/non-mp3 files (for now)
    cd ..
    continue
  fi
  for FILE in *.mp3; do
    TRACK=$(echo "$FILE" | egrep -o ^[0-9]{2})
    ARTIST=$(echo "$FILE" | sed s/^[0-9][0-9]\ // | sed s/\.mp3$// | sed s/\ \-.*//)
    SONG=$(echo "$FILE" | sed s/^[0-9][0-9]\ // | sed s/\.mp3$// | sed s/"$ARTIST - "//)
    # Workaround for eyeD3 bug with UTF8 chars
    eyeD3 --to-v2.4 "$FILE"
    # DO IT!
    eyeD3 --to-v2.4 --set-encoding=utf8 \
      --artist "$ARTIST" \
      --album "$ALBUM" \
      --title "$SONG" \
      --track $TRACK "$FILE" || exit 1 
  done
  cd ..
done

Yeah, it's full of bad practices, but I hacked this in less than one hour and it worked for me and my files. Feel free do adapt for your own messy library. :-)

Edited for legibility.