While you can pick up just about any collection of songs by Schumann, Schubert or Mozart, I tend to stick with the ol' Italian Songs and Arias. I use the
"24 Italian Songs and Arias of the 17th and 18th Centuries" for medium high voice and low voice (two separate books) put out by Schirmer. If I may, I also recommend listening to some singers. For these particular songs you can't beat Cecilia Bartoli. (I actually had the chance to meet her and Renee Fleming in 1998.) Did you know Cecilia played trumpet before becoming a world class Mezzo Soprano? She is also known for having incredible technique. Just listen to her "Vivaldi" recording and there will be no doubt left in your mind. LOL.
I also recommend listening to
Sumi Jo's version of the "Queen of the Night Aria" from Mozart's "Magic Flute". Your jaw will hit the floor. (if you give me an email address, I will gladly send you that sound file). Another great collection for the ears is Kathleen Battle's Mozart album. We can learn a lot about phrasing and musicianship from these singers....but I digress.....uh hem......
Yes, I recommend those Schirmer books. They can be found pretty much anywhere as the repertoire is standard for singers. I am sure you have already found that playing these are great fun and musically satisfying. Whenever I feel stuck musically or want to warm up my sound a bit, I pull a few out and it does the trick. I hope this answers your question.
Kind regards, Alex Yates