Mountain Laurel Designs Duomid? (also check out the Solomid if you don't need space for two people).
Not strictly a tent, but it's extremley lightweight (approx 700g), loads of space for two people and gear, packs down to nothing at all and can withstand some pretty heavy weather. You'll need walking poles though.
I bought one second hand off of eBay along with an Oookworks ground tub. Very pleased with mine!
Top of Helvellyn overnight camp
Blind Tarn overnight camp (howled down with wind and rain all night - stayed dry and warm)