The National Museum of Tequila (Museo Nacional del Tequila, MUNAT) occupies a handsome colonial building on the main plaza and does a thorough job of tracing the spirit's history from its pre-Hispanic roots to its current status as Mexico's most famous export.
The permanent collection covers the cultivation of blue agave, the evolution of distillation technology, and the social history of tequila in Mexican culture. The exhibit on the different categories — blanco, reposado, añejo, extra añejo — is particularly useful if you plan to do serious tasting during your visit. Labels and explanations are in Spanish and English. The museum also hosts rotating art exhibitions, often featuring works by local Jalisco artists.
The museum sits right on the Plaza Principal, so it's an easy first stop before heading to the distilleries.