We started out with a Chicco Cortina travel system and car seat that I got on consignment. The carseat is good, easy to use. Hated the stroller. It was like driving a boat, and it wasn't very portable at all -- we had a station wagon and it didn't even fit in the trunk, we had to also fold down one side of the back seat -- this also meant we couldn't put the carseat in the middle of the backseat.
I traded this in for a new Chicco Keyfit carseat, so got a fresh expiration date (the used one only had about a year left on it) and the Keyfit Caddy when DS was 3 months old. We were getting ready to move so we figured we wouldn't need a whole lot of stroller in the short term.
Once settled in to our new place, we spent some time thinking about what we really wanted in a stroller. We don't have as much space as we did before so ease and compactness of fold was important. We also wanted all-terrain wheels since we are in the park with our dog a lot. And after our experience with the Cortina stroller, we really really wanted something that could fit in the trunk of a small car (we sold our cars and are now doing Zipcar).
We ended up getting the City Mini GT. We can get a car seat adaptor if we want, but DS is now big enough that he is more comfortable outside of his car seat. If we have a 2nd baby we will probably spring for a bassinet attachment for the stroller, since we do a lot more walking with the stroller and we don't use the carseat much.
I think there is a BJ City Stroller that is a double or converts to a double so that could be an option ... we probably won't look to have our 2nd until DS is at least 2, and at that point I might wear the infant while pushing DS in the stroller. There is also an optional glider board that a toddler can ride for short trips, so we might do that. We'll just have to see what works.