My daughter just turned 2 and I have a 5 week old baby. I LOVE my Double Elite Sit 'n Stand stroller from One Step Ahead (onestepahead.com). I used a Sit 'n Stand for the past 2 years with my son and daughter (they are 3 years apart in age) and loved it. Ok, my son loved it because he was 3 when she was born and loved riding on it. My daughter is too young to stand or sit on the back of those strollers, though. But I also didn't want to buy a double stroller that she would outgrow in a year (most kids I know, including my son, want nothing to do with a 'baby' stroller before they turn 3).
This stroller is the best of both worlds. It's a traditional doulbe stroller with 2 reclining seats with 5 point harnesses and sunshades. There's a tray and cupholder for front seat and parent and large storage compartment. It folds easily and is lighter and more compact than most doubles I looked at. When the older child is closer to 3, just remove the backseat (which takes literally less than a minute to do) and it's converted in the bench seat and standing platform for the traditional Sit 'n Stand style.
Pretty much every infant carseat will snap onto the stroller, too, so you can use it with newborns. For the past month I've used it as a double stroller with the infant carseat attached and my 2 year old buckled into the backseat. For 5 months before that, I used it as a normal Sit 'n Stand stroller with my then-4-year-old and then 1-year-old. Because it transforms to a Sit 'n Stand I'll be able to use it for at least another 3 years -- when my middle child is 5 -- and won't have to buy another stroller again.