I recently bought the shareware app iTunes Catalog, which extends the usefulness of iTunes in a number of ways. Check it out.
My initial interest was in producing HTML catalogues of my iTunes library. I discovered after producing a few of these that there were a number of inconsistencies in song tags that I hadn't noticed through iTunes. The most obvious one was albums which had not yet been assigned album art. Another important one was revealing compilation tracks which didn't have the compilation flag set (see my article on this).
I highly recommend this app for its many features, and its new role in ironing out inconsistent tags.