Does anyone know of any vocal solos in Latin, prefferably alto/mezzo range?

it should be a capella or with piano accompaniment. I'm trying to find songs to study next semester, and i'd really like to do something in latin.

Try the "Recordare" from the Mozart Requiem or the "Agnus Dei" from Bach's Mass in B Minor.

You may try "In trutina" from Orff's "Carmina Burana". It's written for soprano voice but, for study purposes, it may be sung by a mezzo voice. The range is between re1 (D1) and re2 (D2). I repeat, it's an idea for study purposes.
You may try also the mezzo arias from Pergolesi's "Stabat Mater". They are beautiful, innocent and deep too.
Also, the cavatina from Rossini's "Stabat Mater".
Cesar Franck's "Pannis Angelicus" (it's written for voice and organ, it may be sung of all the voices).

A really nice one is "Onne Homo ad Alta Voce" ("One man alone in a High Voice"), about the Holy Cross etc. The composer was anonymous 13th century, and I don't know how easy it'd be to find but it's really worth it. I heard it at a concert a few days ago and it's a really beautiful, haunting song. As for accompaniment, it can have a continuo line or not.

Panis Angelicus is a beautiful piece. We learned it in voice class.

Pick up the Liber Usualis or the Graduale Romanum, and you鈥檒l find plenty of Latin solos for your vocal range. ;-)