Larousse Pocket Dictionary : Spanish-English / English-Spanish
A nice sized two way dictionary (meaning you can look up a word in either English or Spanish). Unless you are absolutely fluent or learning some very technical Spanish this dictionary will be more than enough. Each entry has at least one example of the word in use as well, and you all know how much I value examples as a way of learning.
A New Reference Grammar of Modern Spanish by Butt & Benjamin
This is the gold standard of grammar books. It goes into great detail for every point of Spanish grammar and there are many, many examples taken from actual Spanish books, newspapers and street conversations. In spite of the detail it is fairly easy to read, and I actually enjoy just flicking through it (weird, I know). Amazon has a preview of some of the chapters so have look at that and see if you think it would help you with your studies.
Gramática Básica del Estudiante de Español
I bought this book once I arrived in Spain, and it gives the impression of being a text book for use in the Spanish school system itself. All the explanatory text is in Spanish and the examples and excercises are illustrated by lots of cartoons. This actually works very well, and helped me to grasp certain principles such as direct and indirect objects. Each chapter addresses a particular tense or grammatical point and the excercises, examples and illustrations all work together to help you to understand and practice. I’m not sure why the Amazon prices are so high for this one (I bought mine in a shop for €23), but they often have second hand copies for cheaper so it’s worth having a look.