This is why I always say, "Whatever lock will work with whatever object you're locking the bike to." Does no good to have a lock that won't fit around a lamp post if that's the only remaining option.

Of course, that isn't a problem in areas with fewer bikes, but in some places in DC, all the bike racks can be filled, along with many parking meters and other posts.

The lock I use the most often is an OnGuard chain (the "Beast", I think). It's long enough to go through both wheels, the frame and a typical bike rack post. I'm kinda interested in the boron carbide locks & titanium chains that bluefoxicy was talking about on the first page.