One of the most stressful parts of the NYSSMA process for most people is the sightreading portion. However we shouldn't be all that afraid of it and if you give it the time it needs, it won't be nearly as awful as you think.
I recommend the Pinnacle Press Festival Sightreading book.
It is advertised as the Most Comprehensive Sightreading Book Available, and I have a hard time arguing with them. Additionally it is based on the Curriculum for New York State's Solo Festival (NYSSMA). I recommend everyone buy the complete edition which is $34.95 and work their way through the entire book.
I wanted to let you know that I do not get any portion of sales of this book, I just think it is the best one out there for the job.
Sight reading/Singing defined:
I have found that a lot of mis understanding and misnomers about what it is and what it isn't occur. So I want to take a moment to clarify what it means in the context of NYSSMA.
It is the singing of a written piece of music, from beginning to end without stop, that has not been seen or prepared before.