I have one, dont use it much though... it is large and bulky, this one in blue:
Pet Gear PG8150PI Pet Gear Happy Trails Plus Stroller
It was a gift, so I had no choice there... I have used it a few times and it DOES come in handy sometimes but I dont love dragging it out.
I have considered getting one of these:
Pet Gear Travel Lite Stroller - Travel - Dog - PetSmart
I have seen them in the store and they are much lighter to carry around and easier to open and close, mine dont mind being really close, so this would probably be fine for them, even though it is kind of small.