Here is another adjustable dumbbell that lets you go from 5lbs to 50lbs as your body gets stronger. The PowerBlock EXP Dumbbells can be expanded to max weight of 90lbs. These dumbbells work like regular ones but save you a lot of space.
To change the weight, you simply have to slide the selector pin into the blocks at the weight you want, reach inside and grab the handle, and lift it. More info is available here.