Recommended exercise books:
Marchesi, a Theoretical and Practical Vocal Method
Marchesi Vocal Method Opus 31
Lamperti Daily Exercises in Singing,
Panofka 24 Vocalises, and Mozart Solfeggi (only for very advanced singers!).
Listen to this clip of Edita Gruberova singing the Bell Song from Lakme to hear an incredibly perfect vocal technique!
Here is a very interesting article in The New York Times about the state of voice teaching today in the US. I agree with everything in the article and have been saying for years that studying with a teacher once a week is just not enough!