At lunch, colleagues and I went to Tacuba, a recently opened Mexican restaurant in the Bradlee Shopping Center (in the former location of the horrid Desert Moon), a couple miles west of Old Town.
In short....very interesting and very good. Authentic-Mexican style (rather than TexMex) -- the web site (link below) describes it as Mexico City-style. (Having never been to Mexico City, I can't vouch for that.) But, everything we had tasted very spicy and fresh. Highlights from our group: Chicken Tinga enchilada (described as shredded chipotle chicken chorizo and chipotle in adobo), beef barbacoa tacos, open-faced chile relleno, and very good guacamole. Very friendly (though not necessarily efficient) service. The only negative -- it's a touch pricey given the neighborhood.
IMHO, the best Mexican restaurant in Alexandria proper. (Not that there was really much competition to begin with.)