I saw this cool bike on The Gadget Show a couple of years ago and was impressed. It looks and feels like a normal bike but folds down to a compact 35″ x 12″ x 28″. This means you can easily fit it into a car boot or on a train. Although I have a bike rack, I like the idea of this as it is quick and practical and doesn’t compromise on your choice of bike if you like something big with a 700c wheel. They even do mountain bikes. See more at Montague bikes.
The Montague Boston full size folding bike. Other options for Mountain or Road biking are also available.