That's a great question! I reseached far and low and had a very hard time settling on a side by side that had a 50 lb capacity/seat (I have a very tall 3 yr old who is 40 lbs, looks more like a 4-5 yr old) and which had a car seat adaptor I could use with my Chicco cortina infant car seat,for my now almost 3 month old, AND didn't cost more than $500 including the adaptor and other accesories like parent console and kid trays, since unfortunately on top of it all, all these strollers nowadays come with NOTHING. Guess we were spoiled because our Chicco travel system had it all, and we wanted something conparable. We limited it down to the City Mini Double and the BOB duallie, but my husband, who is a big guy, for some weird reason hated the BOB, and so, City Mini it was. We registered for it on Amazon's baby registry, so got 10% off of it, plus we got the 2011 black one, which at the time was for some reason cheaper even than all the other 2010 ones!! with the adapter, the belly bar for when we get rid of the adapter, as well as 2 parent consoles from sunshine Kids, I think they are called, all under $500. On top of it all, I'd registered for Amazon Mom and got 3 free months of Amazon Prime with free shipping, and with our purchase got the max amount of months allowed with their promotion to extend the free shipping for an added extra year (it's been awesome, we've bought several other nonbaby items and gotten free 2 day shipping).
Only bummer, which makes my stroller not the one you need, is that the storage basket SUCKS, it is very small and divided downt he middle, and very hard to get to. But it was the best we could find under the circumstances. I got a sturdy mommmy hook but haven't yet used it to latch the huge diaper bag I carry around. And just last week at Babies R Us I saw a black large diaper bag, don't remember the brand, with an extra long strap that is supposed to be used with the handle bars of double strollers, for $50, so we might go that route...other than that, even though we've only used it a few times at the park, it handles great and is easy to open and close, though it does take an insane amount of space in the back of my Honda Odyssey, especially because of the car seat adaptor, but in a few months we won't be using that part, so it willl be less bulky. Waiting to hear what you finally decide on, and see what other recommendations people had...