Being a mathematics major as well as CS, can offer a recommendation of a book for each of set theory and mathematical logic. Each were the basis for the course I took on the topic, and recieved pretty good reviews on Amazon:
Karel Hrbacek and Thomas Jech, Introduction to Set Theory. ISBN-13: 978-0824779153.
Herbert Enderton, A Mathematical Introduction to Logic. ISBN-13: 978-0122384523.
The Enderton book was what we used for my Mathematical Logic course, and it was pretty good. Thin, but a pretty clear and (apparently) comprehensive presentation.
