I thought it would be helpful for everyone if I highlighted all the places that have wine specials in DC including free corkage or half-price bottles. If you're unfamiliar with the term "corkage", it means that you can bring a bottle of wine with you to a restaurant and they uncork it for you. Most restaurants don't allow this. Some restaurants charge you a fee for uncork the bottle for you, but at some places, they uncork the bottle for free on certain days.

Andale - Half-price bottle of wine with any entree on Monday nights.

Cafe Deluxe - Half-price bottles on Monday nights.

Caucus Room - Free corkage on Friday and Saturday nights.

Chef Geoff's - Half-price bottles, on the last Monday of every month.

Iota - Half-price bottles and glasses on Monday night till 10 PM.

Lavandou - Free corkage Monday nights.

Little Fountain Cafe - Half-price bottles on Wednesday nights.

Melrose Bar - Free corkage on Sunday nights assuming you don't being a bottle that they already have on the wine menu.

Olazzo - Half-price bottles on Monday nights.

Peacock Cafe - Half-price bottles of wine under $60 on Monday and Tuesday nights.

If you get a chance, you should definitely take advantage of any place offering free corkage. You get a chance to take a really nice bottle of wine with you to dinner and save a lot on your bill. Seriously, you can stop at your local wine store on the way to dinner. I actually have a very nice 2001 Flowers Pinot Noir that I've been saving for a night at a place offering free corkage. Maybe I'll stop by Lavandou next Monday and finally drink it.

References:
eGullet
Washingtonian