The Xootr Swift is also an excellent choice,and you can reuse all your componentry aside from the rims. It doesn't fold down as small as some of the other options, so it's not ideal for taking on a bus, but it certainly packs in a suitcase for travel (I've done it several times). it takes about 20 minutes to (un)pack, as there is some minor disassembly involved.
and the ride is fabulous, nearly indistinguishable speed-wise from my road bike. I own two, actually, one with a flat bar and one with drops.