What are some good mathematical magazines and journals for undergraduates and/or high school students? I know only about Resonance published by Indian Academy of Sciences and I've read most of the content from it's math portion of all the issues.

While it is not a journal or magazine, Introduction To Modern Mathematics by Helena Rasiowa is a great book. It covers introductory set theory, logic, and a bit of abstract algebra at the end.
It works through the proofs in detail so it is a very friendly read.
