I’m not a big believer in Spanish dictionaries, but one that I like a lot is DIME: Diccionario inicial del español de México.
DIME is aimed at native speakers of around junior high school age, so it’s a good fit for foreign learners. The number of words (13,000) is fairly small for a dictionary, so you won’t be distracted with low frequency vocabulary. Informal words such as chavo (boy), gringo (American) and verga (cock/dick) are included, but fayuca/falluca (contraband) and latirle (in the sense of ‘like’), are not.
The print is large, which means you can use it not just for consultation but also for casual reading. Several of the entries on plants and animals include drawings. Additional material: spelling and pronunciation guide, verb conjugation tables.
By Raúl Ávila. Published by Editorial Trillas in conjunction with El Colegio de México (2003). 655 pages. ISBN:968-24-6714-4.