If you hit only one sight in Tegus, head here. The museum is housed in the gorgeously renovated 19th-century former Palace of Ministries. It's a superb overview of the nation's history and identity through modern exhibits. Displays are in Spanish, but there are free tours in English by excellent guides four times a day (also ask for French or German tours).
Other great features include a virtual video tour of Copan four times daily and free 2pm movies on various themes every Saturday (hint: June is all about gay pride).