The lightest 3 person tent I am aware of is the MSR Carbon Reflex. But you will pay for it. It is a palace for two, tho.

I would look at that tent, the Tarptent 3 person tents, and at something like the 3 - 5 person 'mid tents (Golite Shangri La, MegaMid from Black Diamond, or other cottage gear 'mids) that have a bathtub floor/bugnet insert - these can be all season, light for the space you get, and you can leave the bugnet home when it's no longer bug season.
_________________________
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

http://hikeandbackpack.com