It really depends on which seats. I've fit 3 across my sister's Chevy Cavalier, my parents' Toyota Camry, my friend's Honda Accord, and my old Saturn SW2 (of those, the Saturn had the least room).
I've found that the Britax Parkway booster fits well in a 3 across situation, as does the Britax Roundabout. Other people have recommended the Graco Ultra CarGo or Platinum CarGo as fitting well next to other seats, too.
SUVs have their place, and if an SUV is the best vehicle for your situation, I hope your husband won't let the "stigma" of SUVs keep him from getting one. (I didn't want an SUV, either, but the Honda Pilot was the safest 8-passenger vehicle available to us when we were buying. I would have preferred a minivan.) Minivans are excellent family vehicles. They tend to be safe, comfortable, and work well with children, so if you will be in a situation where you need to drive more than just 5 people (i.e., if your daughter has a friend over to spend the night), I highly recommend looking at some minivans.