You could always go with something like a Tahoe or Expedition. Mini-vans aren't the only option, but they sure are big and convenient. I'm a big fan of the sliding doors myself.
We have an Explorer. For now it will be plenty of space, when we have more though I'm sure we'll go with a mini-van. My wife already talks about wanting one and we don't even have 1 kid yet. I think she just likes their space.
Four car seats? Oh my! Seriously though are you planning to extend your family anymore than you already have? Most people I know that get the super vans (that can hold 10 comfy) end up not purchasing until they really need it.
