I have the Sit 'n Stand Double Delux from onestepahead.com. It's perfect. You can use it like a normal double stroller (2 reclining seats with 5 point harness, sunshades, foot rests, etc) and then convert it to a Sit 'n Stand design where the child in back can stand or sit facing backwards on the bench. It literally takes just 1 minute to do the conversion. I often change it several times a day when we're out all day, like at the state fair. My 1 year old is in front and the older 2 kids take turns on the back. Sometimes my 3 year old like to recline in the normal seat, other times she likes to stand and even my 6 year old will hop on the standing platform when he gets tired. It works with pretty much every infant carseat out there, too - just snaps in.
It's folds smaller than a typical double stroller and is lighter, too. There's a large basket underneath, tray for front child and a parent tray with a couple drink holders. We've had it for over a year and have used it ALOT. It still looks like new and is easy to manuever even with 80lbs of
Just FYI, they really don't recommend kids using the Sit n Stand feature until around age 3 becuase younger kid tend to hop on/off without warning. Many kids have been injured this way. That's why I got this stroller.... we used it mostly as a double sitting one until my middle child turned 3 a few months ago.