Thanks to the New Liturgical Movement for the link to the Ecclesiastical Latin site. I am delighted to see that there is a "Dictionary of the Psalter". I often speak to students and priests who want to start saying the hours in Latin and I have thought that some time I ought to compile a vocabulary list. It is a great relief to find that this has already been done. Another suggestion that I make is to have a copy of the Douai Rheims bible to hand, open at the book of Psalms. The Dr gives a very literal translation of the Vulgate so it will be helpful for those learning to say the psalms in Latin.
There are many other useful books at Ecclesiastical Latin and some interesting studies such as Christine Mohrmann on the Latin of St Patrick. As a graduate of Reggie Foster, I would add one cautionary note. Do not get carried away by the idea that there is a separate language called "Church Latin" which will suffice instead of something called "Classical Latin". Certainly some of the vocabulary of the christian era would not be immediately intelligible to Cicero and sometimes later Latin messes up the pluperfect passive, for example. Nevertheless, it is better to learn the one Latin Language and enjoy the letters of Cicero alongside the confessions of St Augustine, and the odes of Horace together with the hymns of Venantius Fortunatus.
Christian Latin should not be dismissed (as it sometimes is) as "dog Latin". Compare the Latin of the written tracts of St Augustine with the Latin of his spoken sermons and you will see that he was able to write with great elegance. The same could be said of St Thomas Aquinas. In the Vatican II documents, there is excellent prose in Gravissimum Educationis which helps to make up for the doggerel in Gaudium et Spes.
Speaking of Reggie Foster reminds me of his advice that the most important book to have when learning Latin is a good dictionary. So I am happy to pass on the link (again via NLM) to the searchable online version of that invaluable volume, Lewis and Short's Latin Dictionary.