"Don Quijote Dictionary: Legacy Edition," compiled by Tom Lathrop
This is the Spanish-English dictionary compiled by Tom Lathrop specifically for his student edition of Don Quijote. It's included as an appendix in Lathrop's new Quijote edition, but you can still get it separately here. You can use it alongside any edition of the Quijote, by the way.
ISBN 978-1-58977-101-7 (PB) $8