If you ever want to enter "REM" for the Artist info field, but iTunes keeps auto-correcting it to "ReM" because you have "Red Hot Chili Peppers" in your library, you can enter " REM" and delete the space character.
Note: If the beginning space does not work, try a character that does not exist as an artist's first character in your library.
[robg adds: Since I happened to have both REM and Red Hot Chili Peppers in my library, I tried this, and indeed, iTunes tries to outsmart you. You can see it for yourself by trying to set the artist on any random album to the first two letters (capitalized) of any other artist's name. Another way to fix the problem is to use the back arrow to go back and manually replace the 'e' with 'E'.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040211190245654