*UPDATE 12/2007 - Signature changed locations this year, and I haven't yet seen its new space. I've heard great things, though, and the art direction & management remains the same.*
Signature Theatre is an intimate theater, way-off-Broadway. The configuration changes - it can be in-the-round or black box or cabaret - depending on the show. The shows featured are often world premieres, or special adaptations. The Artistic Director is very proactive here, and isn't afraid of a bit of controversy.
The seats aren't always the most comfortable, but given appropriate advance notice, the house staff is generously accommodating for those with limited mobility.
Wine and beer are available in the lobby during intermissions, along with water and other non-alcoholic drinks. The smoking area is just outside the front door. Parking is not the best - Four Mile Run Drive is a strip of auto garages for the most part - and there isn't a good public transport option, so it's better to get there early and mingle in the lobby area.
Luckily, the nearby Shirlington neighborhood offers some good dinner options, so it's worth making an evening of it. The best of DC's acting community has been featured here (full disclosure: my sister is one of them), and there are Helen Hayes Awards to prove it. See their website for full details and current schedule.