The Red Dragon Book is great (I like it better than the newer Purple edition), however for a gentler intro, I really like Crafting a Compiler[1] by Fischer et al.: the first chapter does a great job of introducing the role of each part of a "traditional" compiler and chapter two implements a complete compiler for a tiny calculator language. The rest of the book follows the traditional progression (scanner, parser, type checking, IR generation, etc.) It's a bit expensive, which is my only reservation when recommending it for a university class (although students are resourceful if you know what I mean ;))

[1] http://www.amazon.ca/Crafting-Compiler-Charles-N-Fischer/dp/...