Dinner in Alexandria
It may have just been an off night, but the last meal I had at La Bergerie was absolutely horrible. And by horrible, I mean every item ordered was bad. If you are looking for excellent cuisine you should go to Restaurant Eve. Besides the delicious food, Todd Thrasher makes the best cocktails in the DC area. You will definitely enjoy your evening there.
In Old Town, I really enjoy Overwood and the Majestic. Both have great food, good atmosphere, and are pretty casual. Do you want a specific area of Alexandria, and are you looking in a certain price range?
220 N Lee St, Alexandria, VA 22314
The Majestic Restuarant
911 King Street, Alexandria, VA 22314
That's a very broad question, then. Here's a quick list, slanted towards Old Town since that's where I've lived for the last 5 years or so:
Southside 815 for southern cooking.
Eamonn's for fish & chips, and PX upstairs Wed-Sat for drinks.
Vermillion & Restaurant Eve for very good upscale dining.
Majestic & Overwood (as suggested above) are nice; Chadwick's is also in the same vein.
Five Guys does an acceptable greasy burger, Austin Grill does the areas best attempt at Tex-Mex, and Hard Times does an OK version of Cinci chili.
There are mediocre-to-OK Thai places every fifty feet or so, it seems, but nothing great. Akasaka off Van Dorn St isn't bad for Japanese, nor is MoMo in Old Town.
Pita House has good Lebanese food; Layla's is also good, but IMHO a worse deal for your $$.
Rustico has good food and great beer.
Hank's Oyster Bar has good (duh!) oysters; I'm also a fan of their fish sammich, although I don't think they offer it on the dinner menu.
Red Mei and Asian Bistro have good pan-Asian offerings (the former is more casual/fast-food style, the latter is sit-down).
For passable BBQ, there's King Street Blues in Old Town, or Red Hot & Blue in Kingstowne (where there are also your usual assortment of chain places like Macaroni Grill).
Finally, if you can cross a city line, go to the western edge of Alexandria and then head another 50 ft west on Duke St, and you'll be in Koreatown, with tons of (again, duh!) good Korean food there, along w/ TemptAsian (an authentic Sichuan place that seems to vacillate between very good and mediocre).