Back in the summer of 2010, I picked myself up a Optek 5-in-1 light reflector on amazon. It was probably the cheapest I could find in the size I wanted with as many modifiers in one piece as possible. It has a diffuser as the innermost circle, with different types of covers for different modifiers. The cover that zips over the diffuser is gold on one side and white on the other side. Then if the cover is flipped it has black on one side and silver on the other. At full size it is 43″ in diameter, but handily it folds down to be 1/3rd that size. Here I have a photo showing all the different modifiers in one. Most of them are self-explanatory as to what they are, but I will say that the diffuser is the one on the floor and the white cover reflector is the one behind my head.
The great thing about these are they can be used for so many different purposes.