Salomaa Arto Salomaa & Rozenberg Grzegorz Rozenberg 
Current Trends In Theoretical Computer Science: Essays And Tutorials [PDF ebook] 

The book is a very up-to-date collection of articles in theoretical computer science, written by leading authorities in the field. The topics range from algorithms and complexity to algebraic specifications, and from formal languages and language-theoretic modeling to computational geometry. The material is based on columns and articles that have appeared in the EATCS Bulletin during the past two to three years. Although very recent research is discussed, the largely informal style of writing makes the book accessible to readers with little or no previous knowledge of the topics.