a vestibule will keep your stuff dry if your on level ground and not in a torrential downpour...
I'm a fan of just a tarp under the bag and stars above
but have a northface tadpole tent, 2 person pretty easily, and you can fit some gear in there if your sleepin really close to the other person in there. and it has a vestibule as well.
check out
http://www.sierratradingpost.com/ they always have some stuff on clearance and good prices on most of their non clearence stuff.