I can vouch for TaPL - I can see it on my bookshelf from here. It's a great overview of the foundational concepts in PLT; Pierce's style is remarkable, he write

I can vouch for TaPL - I can see it on my bookshelf from here. It's a great overview of the foundational concepts in PLT; Pierce's style is remarkable, he writes the most readable academic text I've ever seen. (I also own & admire his Basic Category Theory for Computer Scientists; I'm yet to brave his Advanced Topics in TaPL - I'm sure it's very good, but the contents list intimidates me.)