Inglesina's Twin Swift
Don't shy away from side-by-side double strollers out of concern that they won't go through a door; none is wider than a wheelchair, so all fit standard entrances. They fold flatter than front-to-back models, making them easy to store and travel with. Kids ride next to each other, which has its pros and cons; a definite plus is that you can easily reach them both.
Inglesina's Twin Swift is a workhorse; the seats, baskets, and wheels withstand heavy use. Two bags can hang on the back ($250; babiesrus.com).